2 Corinthians 13:14 The grace of the Lord Jesus Christ, and the love of God, and the communion of the Holy Ghost, be with you all. Amen.
Perhaps no single verse in the Bible can be said to “prove” the doctrine of the Trinity. But if one has their wits about them, it ought to be passing strange that such associations of the three Persons, God the Father, the Lord Jesus Christ the Son, and the Holy Ghost or Holy Spirit are associated together throughout the Bible (see Matthew 28:19; 2 Corinthians 13:14; Isaiah 42:1) just as though they indeed belong together, and are mentioned on a footing of equality. Because of this feature in the Bible, those who have studied this issue carefully, by the Rule of Necessary Inference, believe in the Bible doctrine of the Trinity.
Unitarians, Jehovah’s Witnesses, and Muslims do not believe in the doctrine of the Trinity. They all argue strongly against it in their support of Monotheism. But to deny the Trinity, they must ignore or suppress the evidence in the Bible that contradicts their position, and often turn some Scriptures upside down or on their head with strange, out-of-context interpretations that are unsupported by a clear reading, a plain reading, of the text itself in context.
There is an article linked on the “Islam and Christianity Debate Group” discussion thread titled “Ten Ways the Bible Disproves the Trinity” LINK which I intend to answer here, rather than on Facebook, because it always takes more words to answer a mistaken opinion or argument than it does to present it.
TEN WAYS THE BIBLE DISPROVES THE TRINITY ANSWERED:
Now, if the Trinity represents the truth about the nature of God Almighty, and was preached by Jesus (peace be upon him), then one would expect this to be reflected clearly throughout the Bible. Moreover, one would not expect to find anything which negates the doctrine. What follows are ten reasons, taken from the Bible, that disprove the doctrine of the Trinity.
1. God does not change.
Anyone who speaks a word against the Son of Man will be forgiven, but anyone who speaks against the Holy Spirit will not be forgiven, either in this age or in the age to come. [Matthew 12:32]
Apparently the Muslim apologist I am citing is unaware that each member of the Trinity has its unique offices and responsibilities. Jesus taught that one of the offices or responsibilities of the Holy Spirit is to reprove or convict and convince men of their sinfulness, of their sin (John 16:8). In Matthew 12:32 and its context, the Jewish leaders were refusing to believe in and accept Jesus Christ, even though He (1) healed the sick, (2) forgave sin, though only God can forgive sin–yet by their own postulates, the Jews believed that only God could heal, so Jesus proved He can do both, see Mark 2:5-8; (3) had power over nature itself when He calmed the storm at sea, see Mark 4:31-41; (4) possessed creative power demonstrated when He multiplied the loaves and fish to feed five thousand men besides women and children, see Mark 6:37-44. In context at Matthew 12:32 the Jewish authorities were attributing to the power of Satan what was evidently done by the power of God, thus they were resisting the conviction based upon tangible evidence brought by the Holy Spirit. This sin was unforgivable then and if persisted in by anyone today who refuses the testimony of the Bible to the Person of Christ that He is without question the Divine Son of God, the Savior of the world, is unforgivable today, and will result in the loss of salvation and a most unfortunate eternal destiny where “the fire is not quenched” (Mark 9:47, 48).
4. Jesus acknowledges that he has a God.
Jesus said, “Do not hold on to me, for I have not yet ascended to the Father. Go instead to my brothers and tell them, ‘I am ascending to my Father and your Father, to my God and your God.’” [John 20:17]
I am coming soon. Hold on to what you have, so that no one will take your crown. The one who is victorious I will make a pillar in the temple of my God. Never again will they leave it. I will write on them the name of my God and the name of the city of my God, the new Jerusalem, which is coming down out of heaven from my God; and I will also write on them my new name. [Revelation 3:11-12]
Jesus Christ in His human nature certainly speaks of God the Father as “my God.” This is very correct. Yet Jesus Christ even now still possesses, since the Incarnation–His having become a man–a human nature. For all eternity forward He is and will always be a man. He is called “the man Christ Jesus” well after His ascension to heaven in 1 Timothy 2:5. The hypostatic union continues forever. Subordination does not imply inequality. It simply reveals the arrangements among the Persons of the Godhead, the Trinity, as to their respective offices with respect to the redemption or salvation of mankind.
Therefore, the fact that Jesus Christ acknowledges that He has a God is no argument against the doctrine of the Trinity.
5. Jesus surrenders his kingdom to God.
Then the end will come, when he hands over the kingdom to God the Father after he has destroyed all dominion, authority and power. For he must reign until he has put all his enemies under his feet. The last enemy to be destroyed is death. For he “has put everything under his feet.” Now when it says that “everything” has been put under him, it is clear that this does not include God himself, who put everything under Christ. When he has done this, then the Son himself will be made subject to him who put everything under him, so that God may be all in all. [1 Corinthians 15:24-28]
Here is a case of assuming what is to be proved. The text of Scripture as cited from 1 Corinthians 15:24, 25, 26, 27, 28 does not state that Jesus hands over his kingdom to God, but rather “the kingdom.” This is a very interesting instance of a Figure of Speech used here that exhibits “intentional obscurity.” This means that when the Apostle Paul penned these words he purposely wrote this text to be obscure to avoid persecution from either Jewish or Roman authorities (see John 11:48; Acts 17:7) should this letter fall into the wrong hands. See my note at 1 Corinthians 15:24 in my book, The New Treasury of Scripture Knowledge, for a full discussion of this passage and examples of other instances of “intentional obscurity” in the New Testament.
Jesus does not give up His own kingdom, but those kingdoms He has subdued (Revelation 11:15), for the Messianic Kingdom on this earth will never end (Daniel 7:14; Luke 1:32, 33).
6. Not defined anywhere in the Bible.
One of the teachers of the law came and heard them debating. Noticing that Jesus had given them a good answer, he asked him, “Of all the commandments, which is the most important?”
“The most important one,” answered Jesus, “is this: ‘Hear, O Israel: The Lord our God, the Lord is one. Love the Lord your God with all your heart and with all your soul and with all your mind and with all your strength.’ The second is this: ‘Love your neighbour as yourself.’ There is no commandment greater than these.”
“Well said, teacher,” the man replied. “You are right in saying that God is one and there is no other but him. To love him with all your heart, with all your understanding and with all your strength, and to love your neighbour as yourself is more important than all burnt offerings and sacrifices.” [Mark 12:29-33]
To argue that “Scripture should provide” a clear explanation of these matters is an appeal, in part, to the principle of “rationalism,” which when it comes to understanding what the Bible has to say is a false principle. Who are we to demand that God rewrite the script to suit our way of thinking, our demands?
Even the Scripture writers themselves testify that they did not fully understand what the Holy Spirit inspired them to write (see 1 Peter 1:10, 11, 12 and Daniel 8:15).
The Bible is not written in the form or format of a systematic theology. To learn its truths we must “Search the Scriptures” (John 5:39; Acts 17:11). To determine what the Bible actually teaches about a subject of interest to us, we must take into account all that the Bible says or reveals about that subject, and often related subjects. Not everything about a given subject of interest is necessarily stated all in one passage of the Bible.
To do Real Bible Study, therefore, we must use appropriate tools for Bible study, such as Bible concordances and collections of cross references given in reference Bibles or The Treasury of Scripture Knowledge, or my expansion of that well-received venerable work, The New Treasury of Scripture Knowledge or my work Nelson’s Cross Reference Guide to the Bible. I have now finished preparing a new work which is far more complete and accurate than the previously named resources, but I cannot tell you the title of it yet because the title has yet to be determined.
Trinitarians do not merely “cobble together bits and pieces of scripture in order to try and form a picture of a Triune God.” Rather, we carefully study Scripture according to the Rules of Interpretation given here in the October 2010 Archives listed to the right on this page. We read carefully, and by drawing the proper necessary inferences, we arrive at the truth of what the Bible teaches.
The Jews of the time of Jesus Christ were expecting a Messiah. They thought they knew their own Scriptures well. They knew about messianic prophecy in the Hebrew Scriptures. Yet, they either failed or refused to recognize the Messiah when He came at the appointed time and manner revealed in Scripture. Humanly speaking, they failed to draw the Necessary Inference about the coming Messiah when they did not observe two different classes of messianic prediction found in the Hebrew Scriptures, our Old Testament. What they failed to see, even refused to see, was that Messiah must first suffer, and only then enter into His glory (Luke 24:26; 1 Peter 1:11).
The same procedure in careful Bible study required to properly gather and understand messianic prophecy is the method that must be employed to learn the truth about the Bible doctrine of the Trinity.
The Jews failed at both.
7. Fabrications inserted into the Bible to support the doctrine.
An appeal is made to the text of 1 John 5:7 as it stands in the King James Version and its underlying Greek text, a text known as the Received Text.
Since no one appeals to this passage today to support the doctrine of the Trinity, such an argument is moot. It has nothing to do with the truth or alleged falsity of the doctrine of the Trinity. There is plenty of other evidence in the Bible for the Trinity.
8. Trinitarian scholars manipulate the Bible to protect the doctrine.
Now this is eternal life: that they know you, the only true God, and Jesus Christ, whom you have sent. [John 17:3]
“This is eternal life, that they may know Thee and Jesus Christ, whom Thou hast sent, as the only true God.” 
Most Christians today are unlikely to know of this information about Augustine’s citation of the text of John 17:3. I do not know of any contemporary scholarship that handles John 17:3 this way.
But I would assert that The New World Translation produced by the Jehovah’s Witnesses most certainly does “manipulate the Bible” to protect their anti-Trinitarian doctrine. They mistranslate John 1:1 to read “and the word was a god.” They carefully eliminate every reference to the Holy Spirit as a Person. And much more. So when it comes to just who it might be in our day that would manipulate the very text of Scripture to support false doctrine, it would seem that Jehovah’s Witnesses have clearly done just that.
9. God is above Jesus in hierarchy.
But I want you to realize that the head of every man is Christ, and the head of the woman is man,and the head of Christ is God. [1 Corinthians 11:3]
If only it were that simple, the argument might be swung in favor of the Muslims, Unitarians, and Jehovah’s Witnesses and their denial of the Trinity.
As I stated above, this is an argument based upon rationalism. It seeks to rewrite the script. It fails because it cannot account for other things Paul wrote that declare precisely the contrary (Romans 9:5; Titus 2:13, etc.).
The persons of the Trinity are revealed in Scripture to each assume particular offices and roles in the Godhead. That God the Father assumes a position in hierarchy above Jesus the Son of God does not disprove the doctrine of the Trinity. Subordination does not imply inequality.
10. Necessitates the belief in three gods.
Now the Pharisees who had been sent questioned him, “Why then do you baptize if you are not the Messiah, nor Elijah, nor the Prophet?” [John 1:24-25]
Of course this comparison misses the point completely. When the Jehovah Witnesses came to visit me for four years, they had a similar numerical argument against the Trinity. How, they asked, can 1+1+1 = 1? I said, simple. Consider that 1x1x1 = 1. What Biblical authority can you cite to require addition rather than multiplication? The argument either way has no validity to what the Bible teaches about the Godhead consisting of Three Persons, each of whom is called God in Scripture itself, and each of whom possess the several incommunicable attributes of God. But since only God can possess these incommunicable attributes, yet Scripture attributes them to both Jesus the Son of God and to the Holy Spirit, as I have frequently posted on this site from my note on Matthew 28:19 in The New Treasury of Scripture Knowledge, we have positive proof for the doctrine of the Trinity that it is plainly taught by Necessary Inference in Scripture itself.