Whenever we begin talking about the Trinity it is understandable that there is some confusion.  When we say, God is Triune, most people think "1 + 1 + 1 can not equal 1".  But the fact is God is Triune.  There is only one God, but He is in Three holy and equal Persons.

We can use many illustrations to try to explain the Trinity.  But all are inaccurate and insufficient in some way.  For instance, the Supreme Court is made up of nine Justices, each with equal power.  Yet there is not nine Supreme Court's but only one.  In another example we can take three vials of liquid, each with the same properties.  When we mix the three vials the liquid still has the same properties, though its content is now three and not one.  There are indeed many ways to illustrate the Trinity through the world around us.  But all ways are somewhat imperfect, leading to confusion.

One point we can make is that: though the Trinity is hard to illustrate, the Bible specifically teaches this doctrine.  Once you see the Biblical arguments you will see that, without the Trinity, God can not exist.
 

The Jews often quote the above passage to prove that God is not in three Persons but only One.  What is often neglected is that there are two different words in the Hebrew used for one.

YACHID, meaning an absolute unity or properly '1'.  This word's use is illustrated in Genesis 22.2, where God said to Abraham:

Genesis 22:2  "And he said, Take now thy son, thine only (YACHID) son Isaac, whom thou lovest, and get thee into the land of Moriah; and offer him there for a burnt offering upon one of the mountains which I will tell thee of. "

The word YACHID is never used in the Bible for the Godhead.

ECHAD, meaning a compound unity, several composites which make a whole or a combined '1'.  We can define this word's usage in passages such as:

Genesis 1:5  "And God called the light Day, and the darkness he called Night. And the evening and the morning were the first (ECHAD) day."

ECHAD  is also found in Genesis 2.24, where we read:

Genesis 2:24 "Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one (ECHAD) flesh. "

ECHAD  is also used of God in Deuteronomy 6.4 and in many other passages that refer to the compound unity of the Godhead.  When we compare ECHAD as used in other passages to  Deuteronomy 6.4 we see that God is not an absolute One but a compound unity. This unity is made up of three Persons. Just as Day is made up of evening and morning, and one flesh is made up of man and wife, the Godhead is composed of Father, Son, and Spirit.

In other passages we see clear presentations of the Doctrine of the Trinity:

Isaiah 48:12-16 "Hearken unto me, O Jacob and Israel, my called; I am he; I am the first, I also am the last. Mine hand also hath laid the foundation of the earth, and my right hand hath spanned the heavens: when I call unto them, they stand up together. All ye, assemble yourselves, and hear; which among them hath declared these things? The LORD hath loved him: he will do his pleasure on Babylon, and his arm shall be on the Chaldeans.  I, even I, have spoken; yea, I have called him: I have brought him, and he shall make his way prosperous. Come ye near unto me, hear ye this; I have not spoken in secret from the beginning; from the time that it was, there am I: .... "

So far in Isaiah's text we see God speaking.  It couldn't be anyone but God, for He describes Himself as the  first, I also am the last. He uses God's Divine title of I am he.  This denotes His eternality, His forever existence (Exodus 3.3).  He also claims to be the Creator of the Heavens and the earth.  God is clearly speaking here, but in last part of the text, without changing context, God says:

 ".. and now the Lord GOD, and his Spirit, hath sent me .."

Notice that God says that God sent Him.  In fact, God says that God and His Spirit sent him.  This is nothing less than an Old Testament vision of the throne room of God.  In the throne room the One God sent Jesus to be man's redemption.  The other Being present was God the Spirit.  They both sent Christ so that man might be saved.

Isaiah 43:10-11 "Ye are my witnesses, saith the LORD, and my servant whom I have chosen: that ye may know and believe me, and understand that I am he: before me there was no God formed, neither shall there be after me. I, even I, am the LORD; and beside me there is no saviour. "

When we say Trinity you are not to assume that we are saying there are three God's.  There is but One God in Three Persons.  The Father is God.  The Father and the Son is God.  The Father, Son,  and Spirit are God.  They are Three Persons, each with distinct personalities.  Neither the Father, Son, or Spirit are created but are self existent.  There was never anytime in eternity that all Three did not exist in perfect unity: no one member of the Godhead existed before the other.

Matthew 1:21-23 "And she shall bring forth a son, and thou shalt call his name JESUS: for he shall save his people from (APO, from the ultimate source of) their sins. Now all this was done, that it might be fulfilled (PLEROO, Aorist Passive Subjunctive, To fill up a deficiency once and for all) which was spoken of the Lord by the prophet, (This was one of the three great warnings Isaiah would give to the Jews living between 63 and 70 AD. He warned of the Virgin birth [Isaiah 7.14], of the unique crucifixion of the Savior [Isaiah 53.9], and of the outpouring of Tongues and the Gifts [Isaiah 28.11]) saying, Behold, a virgin (PARTHENOS, one specifically a virgin, having had no sexual expression. The Hebrew parallel, HA ELMA, is found in Isaiah 7.14) shall be with child, and shall bring forth a son, and they shall call his name Emmanuel, which being interpreted is, God with us. "

Though Jesus was born through virgin pregnancy and birth in the flesh, in His Spirit He was Eternal God.  The Scripture clearly states His birth was a fulfillment of God with us, the Prophecy of Isaiah 7.14.  If Jesus was only a god among many lesser gods (as the Mormons and several other cults would have us to believe), then Isaiah 43.10-11 is obviously a lie.  If Jesus was not God (as the Way International and other cults would have us to believe), but only a "good man", then Matthew 1.21-23 and Isaiah 7.14 is a lie.  If God is not Triune, as the Jews and the Christian monotheists would have us to believe, then Isaiah 48.12-16 is a lie.  Or God is indeed Triune, One God in Three distinct Persons, and all three of these verses are the inspired word of God.

1 Corinthians 3:16  "Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you? "

If we are the temple of God then God must dwell in us.  Who else would dwell in the temple of God but God?  And if the Holy Spirit is the One who indwells the temple of God, then He must be God.

Acts 5:3  "But Peter said, Ananias, why hath Satan filled thine heart to lie to the Holy Ghost, and to keep back part of the price of the land? "

Who did Ananias lie to?  He lied to, the text plainly states, the Holy Ghost.  Now I want you to note the rest of the context:

Acts 5:4  "Whiles it remained, was it not thine own? and after it was sold, was it not in thine own power? why hast thou conceived this thing in thine heart? thou hast not lied unto men, but unto God."

The Jehovah's Witnesses and other cults have preached for years that the Holy Spirit is a power of God, but not God himself.  But Acts establishes a parallel that destroys this theory:
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These are pretty clear texts on the deity of the Holy Spirit, so let's see Biblical proof that Jesus is God the Son.  There is very good proof of Christ's deity found in the Book of Revelation, if you follow the entire context.

Revelation 21:4-7 "And God shall wipe away all tears from their eyes; and there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain: for the former things are passed away. And he that sat upon the throne said, Behold, I make all things new. And he said unto me, Write: for these words are true and faithful. And he said unto me, It is done. I am Alpha and Omega, the beginning and the end. I will give unto him that is athirst of the fountain of the water of life freely. He that overcometh shall inherit all things; and I will be his God, and he shall be my son. "
 
We need to clarify several things about this verse before we continue our study.  The text clearly states that the One sitting on the throne is God, and God applies two titles to Himself, Alpha and Omega, the beginning and the end.  What I am about to save may sound silly, but because of the cultists I must say it.  You cannot have two Alpha and Omegas.  You cannot have two beginning and ends.  God is sitting on the throne and says He is the beginning and the end.  If he is the beginning and the end, then He is ultimately so.  Understand this and the rest of the context is easy.  Now turn to Revelation 22, where we read:

Revelation 22:12-14 "And, behold, I come quickly; and my reward is with me, to give every man according as his work shall be. I am Alpha and Omega, the beginning and the end, the first and the last. Blessed are they that do his commandments, that they may have right to the tree of life, and may enter in through the gates into the city. "

Now again, stop and note several things.  First, this is God talking here.  He again calls Himself Alpha and Omega, the beginning and the end, the first and the last.  The text adds that God says I come quickly.  Who is this One who calls Himself God,  and He is coming quickly?  This is explained in the next verse:

Revelation 22:16  "I Jesus have sent mine angel to testify unto you these things in the churches. I am the root and the offspring of David, and the bright and morning star. "

We know that the One coming quickly is Jesus Christ from paralleling this text to:

1 Thessalonians 4:13-17 "But I would not have you to be ignorant, brethren, concerning them which are asleep, that ye sorrow not, even as others which have no hope. For if we believe that Jesus died and rose again, even so them also which sleep in Jesus will God bring with him. For this we say unto you by the word of the Lord, that we which are alive and remain unto the coming of the Lord shall not prevent them which are asleep. For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first: Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord. "

.. and the one coming quickly is God, according to Revelations.  Jesus further identifies Himself, without a change of context, as God.  So Jesus is God!

Why did I make the statement earlier that there cannot be two Alpha and Omegas, beginning and ends?  Because the cult argument against this proof is that God the Father is coming back with Jesus who is the lesser god.  But the One coming back is says He is the Alpha and Omega, the beginning and the end.  Either we have two Alpha and Omegas, beginning and ends, which is impossible, or the One God returning is Jesus Christ and the Doctrine of the Trinity is true.  Choose either confusion or the Trinity.  There is no in between choice, for any other choice is reputed by Scripture.
 

The reason that Christian Monotheism is particularly difficult to refute is that they use many Trinitarian proofs of God in reverse.  For instance, there are many parallels between the Old and New Testament that prove that Jesus is God.  The Monotheist will find a verse in the Old Testament and say that "God is the only Savior": and in the New Testament that "Jesus is the only Savior".  If God is the only Savior, then Jesus must be the only God.  Since Christian Monotheism twists many of the Trinitarian texts it is hard to refute them.  Also, if a Trinitarian text is used prove that there is a Trinity,  Christian Monotheism responds with "That's just an Old Testament manifestation of Jesus Christ".

Christian Monotheism is a growing religion because the Doctrine of the Trinity is so hard to understand.  How can Three be One?  Honestly, many people cannot understand this.  But I know that the Trinity is a fact fully supported by Scripture.  I can equate the Doctrine in my mind, but I do not understand it completely.  It just is, because the Bible says it is!  The Christian Monotheist responds with, "Since I cannot understand it, it cannot be true.  Three cannot be One.  One can only be One, and that one is Jesus Christ".  But few people understand how an Atomic Furnace works, nor do we understand how electricity works or how an atom holds itself  together. These are all mysteries that science cannot fully explain: It just is!  We know that electricity works but how is a mystery.  Because it is mystery should we suddenly stop using it because we do not understand it?  Because it is a mystery should we stop believing in it?

Christian Monotheist takes it's stand against Trinitarianism because of what the Reformers did not do.  They state that Trinitarianism was inherited from a corrupt Catholic Church, and that the question of the Godhead was never severely considered by the Reformers.  They believe that Trinitarianism became a tradition passed down to the Protestant Church, and entering without dispute just as did the holidays of Christmas and Easter. But just because a religion taught false doctrine in some areas doesn't mean that the same religion was off base in all areas. There are many true Biblical doctrines taught by the Catholics that the Protestants also support. The Christian Monotheists teach that you must be baptized to be saved, yet this doctrine is totally unsupported in Scripture, yet in other areas they are doctrinally correct. We must be careful to not allow sectarianism to prevent us from accepting the full truths of the Bible. As for the statement that "The Reformers never seriously considered the Doctrine of the Trinity", this is untrue. John Calvin, for example, extensively examined Trinitarian Doctrine and concluded it was fully Biblical. I refer you to Calvin's Institutes of the Christian Religion, sections 1.13; 1.15.3; 2.14.3; 2.14.5-8; 2.15.5; 3.4.26; 4.15.6; 4.15.16, 19; 2.14.1-8.

There are many verses that we have previously studied that can be used to disprove Christian Monotheism.  The passage in Isaiah that represented Three Distinct Persons as God is one that disproves the "manifestation" theory.  Other verses in the Bible show God sending the Son into the world, and the Son sending the Spirit.  How can God direct himself?  How can order Himself?  Talking to yourself and telling yourself to go here or there are symptoms of schizophrenia, and my God is not crazy.  Either God is mentally incapable, going to great lengths to act out three parts so as to deceive mankind, or He is indeed Triune.  There is no middle ground.
 

If you cannot understand this line of reasoning then there are other simpler proofs of God's Triune nature.  These proofs are found when you see the necessity of the Doctrine of the Trinity as it influences and is supported by other Bible doctrines.

First, the Doctrine of the Trinity is essential for any lasting plan of redemption for man:

2 Corinthians 5:19  "To wit, that God was in Christ, reconciling the world unto himself, not imputing their trespasses unto them; and hath committed unto us the word of reconciliation. "

Since the fall of Adam the foremost theological discussion has been, "How can men become reconciled to God?  Man, by his own volition, chose to follow Satan.  Man must pay the penalty.  But how can man pay the penalty of the Fall?

Some say that since we were not there at the Fall we were not accountable.  But to say this is to oversimplify the problem.  When God created man in the Garden he was perfect, without sin.  When man disobeyed God he fell into sin and Spiritual death.  Our children are genetic replicas of what we are.  If the parents are black the child will be black.  If the parents are white the child will be white.  Though the combinations of parents do not always produce the expected child, this is the norm.

When Adam walked the earth before the Fall he was without sin, and had a functioning human spirit.  This human spirit enabled him to physically communicate with God at will.  God walked in the Garden every day just to talk to Adam face to face.  After the Fall Adam became spiritually dead, and this relationship was lost.  Residing in him was sin, the old sin nature.  As Eve was also spiritually dead when they came together to reproduce their offspring were also spiritually dead.  Can a dead tree produce a live tree?  Death only produces death.  The offspring of Adam were all genetically spiritually dead, having the old sin nature from birth.

So here is the dilemma.  By the fall mankind met spiritual death.  God, in his justice, required that man pay the penalty for the Fall.  But man was not fit payment before God.  Before a man could repay the penalty of sin for the human race he had to pay the penalty for himself.  And since man was spiritually dead there was nothing that he had that God wanted.  The dead cannot contribute to the living.  The spiritually dead cannot pay back the penalty of spiritual death.

A substitution could pay the penalty for sin.  One could pay the penalty if he was first clean himself.  But the substitution must first be clean or else it would not be acceptable before God.  The problem was that there was no one in humanity who could pay back the penalty, because all mankind was spiritually dead.  The parents might raise a morally right child,  but parents could not produce an offspring that was without the old sin nature and spiritual death.

God knew the fix that man was in.  God had every right to destroy the human race and start over.  But if He destroyed man because of Satan's deceit, then Satan would have won a battle against God. Thus God set out to show that, regardless of what Lucifer did, He could right the situation.

But God was not ready to bring man out of spiritual death just yet.  The old sin nature brings with it an inflated ego, leading man to think that he can become righteous before God with his own works.  To disprove this God set up a system of works whereby man could see how utterly impossible it was to get to Heaven by his own efforts.  God set up the sacrifices first as a means of temporary atonement for sin.  If man obeyed God by offering the animal sacrifices religiously, then God would tolerate the fallen state of man for a time.  If man refused to obey by refusing to offer the animal sacrifices, then God classified him as an unbeliever and a heathen.  After physical death this group of people went to Hades without hope of redemption.

God set up another system of works that complemented the sacrifices.  This system was called the Law and was composed of about 2500 statutes of do's and don'ts.  Each day you woke up you had to face a strict system of religion.  If you broke the Law, then you atoned for this by making an animal sacrifice.  On top of all this once a year you had to make a sacrifice to atone for portions of the Law you broke and forgot to atone for.

This system was less than satisfactory, and God knew it.  But He wanted to leave the system in place until men knew it as well.  Mankind must understand that there is nothing that we can do before God to get out of the mess we're in.  Mankind had to know that he could not pay the penalty, for man was totally filthy before God.

Man was between a rock and a hard place.  Man need to pay the penalty for sin but could not.  God was the only One who could pay the penalty.  Hence the Trinity.  God had to solve the problem of man, but as Man and not God.  God lowered Himself to become Man in the Person of Jesus Christ.  Since Jesus as God was sinless, When He took on flesh as God-Man He was also sinless.  He went to the Cross as a Man to pay for our sins.  He rose again on the third day to show that the payment was acceptable to the Godhead.  While on the earth as a man, Jesus used to the powers of the Spirit to perform miracles, to teach, and to lead people to salvation in Him.

But this is not the entire story of redemption.  When man was allowed to temporarily redeemed himself through animal sacrifices, none of the sacrifices had any lasting value.  Not only was the sacrifice improper in itself (for an animal cannot pay the penalty for men), but as soon as the sacrifice was made man went back out and began to sin again.  We are all compulsive sinners.  Even as a hermit man will still find a way to sin.  Again comes the Trinity of God to the rescue.  Christ is seated at the right hand of God the Father forever, making intercession for our sins:

Hebrews 7:22-28 "By so much was Jesus made a surety (EGGUOS, guarantee) of a better testament (DIATHAKA, covenant). And they truly were many priests, because they were not suffered to continue by reason of death: But this man, because he continueth ever, hath an unchangeable priesthood. Wherefore he is able also to save them to the uttermost that come unto God by him, seeing he ever liveth to make intercession for them. For such an high priest became us, who is holy, harmless, undefiled, separate from sinners, and made higher than the heavens; Who needeth not daily, as those high priests, to offer up sacrifice, first for his own sins, and then for the people's: for this he did once, when he offered up himself. For the law maketh men high priests which have infirmity; but the word of the oath, which was since the law, maketh the Son, who is consecrated for evermore. "

When we sin now, rather than being "saved again", Christ immediately makes intercession for us.  This ensures that we retain our salvation rather than lose it.  God the Holy Spirit also indwells us, aiding us in making better decisions for the Lord, and convicting us to repent when we sin.  Only through the Trinity are we maintained in God's redemption.

The Christian Monotheist would tell us that the Jesus manifestation makes intercession with Himself, which is nonsense. The Mormons and Jehovah's Witnesses say that the "lesser god" Jesus makes intercession for our sins.  But a mediator or intercessor must be equal with both parties that He tries to reconcile.  If Jesus was merely a man He could not be an Intercessor, for He would not be equal with God.  If Jesus was pure God then he would not be equal with man.  If Jesus were lesser god that he would not be equal with either God or man.  Jesus must be pure God in the flesh, forever sitting at the right hand of God the Father in Heaven.  Any other combination throws our salvation away.  The Doctrine of the Trinity, though many may not understand it, is true. It is a foundational Doctrine in the Christian faith that cannot be lightly thrown away because of Catholic prejudice.