Is Belief in the Trinity Supported by Scripture?

Many Christians believe that God is three beings in one, where Jesus was a human manifestation of one of those beings. The Westminster Confession presents it as:

“In the unity of the Godhead there be three persons, of one substance, power, and eternity: God the Father, God the Son, and God the Holy Ghost: the Father is of none, neither begotten, nor proceeding; the Son is eternally begotten of the Father; the Holy Ghost eternally proceeding from the Father and the Son.” (Chapter 2, section III)

This conflicts with the approach set out in the Old Testament by: “…the Lord is one.” (Deut. 6:4), “I am the first and I am the last, and besides Me there is no other” (Isaiah 44:6). It is also in untenable from the New Testament, conflicting with much of what Jesus allegedly taught. (Cf. John 5:30, 20:17, Matthew 12:31-32, 20:23, Mark 13:32, Luke 22:42)

You will note that the prophet Isaiah asserted in several of his discussions about idolatry that God simply does not have a human form. In contrasting God to the false gods he stated:

^“Verily Thou art a God that hidest Thyself, O God of Israel, the Saviour. They shall be ashamed, yea, confounded, all of them; they shall go in confusion together that are makers of idols.”

(Isaiah 45:15-16)

It is clear that the unique quality of the God of Israel is that he is "hidden", not possessing human form (Cf. Isaiah 40:18-19 where the same contrast is made.).

The Old Testament teaches the God revealed Himself to the Jewish people at Mt. Sinai with the words:(Exodus 20:2) “ I [am] the LORD thy God, which have brought thee out of the land of Egypt, out of the house of bondage. Thou shalt have no other gods before me”. This revelation is all inclusive; it contains both the information of whom to worship as well as whom not to worship. This is where God sealed all theological beliefs. Anything not included therein is termed as idolatry. This revelation was instructed to be propagated to the descendents of that generation of Jews by Moses in the verse: (Deut. 4:10) “[Specially] the day that thou stoodest before the LORD thy God in Horeb, when the LORD said unto me, Gather me the people together, and I will make them hear my words, that they may learn to fear me all the days that they shall live upon the earth, and [that] they may teach their children.” Hence, it is clear that there will be no more information about God that is forthcoming 1000 years later.

What’s most important, is that throughout Scripture whenever the Jews are instructed whether a particular belief is acceptable, the test is always: (Deut 13:16 et. al) “other gods, which thou hast not known, thou, nor thy fathers;”. Since the Jews had never been shown a Triune God, they never would have permitted to accept one. The handful of Christian “proofs” to a Triune God contained in Hebrew Scripture are certainly not adequate proof that the Jews believed it for two reasons: 1)any of them can be refuted someone with a modicum of Hebrew knowledge; 2) none of them are demonstrative enough to indicate beyond any doubt that God revealed himself as Triune. A concept so fundamental to belief would never have been merely “hinted” at in a handful of verses. The suggestion that a Triune God was revealed to the Jews and somehow over the course of time “forgot” (some sort of mass amnesia) or that they simply started lying at some point in history is absurd for the following reason: if the Jews are simply people who invent their own principles and sources, then Christians would be forced to reject the Old Testament prophecies and Scriptures. The choice of which books are included, which prophets were valid, what text is accepted, was all made by this same nation that Christians are claiming as flagrant liars.

For Christians to accept the Hebrew Scriptures which were held closely to the nation that they accuse of lying up until the late 1^st century while rejecting the testimony of the Jewish nation as a whole is nothing but sheer hypocrisy.