Biblical Unitarian faith in the Father of Jesus as the One who alone is truly God, is not new.

The whole of the Old Testament speaks of this one God in unequivocal terms. THERE IS NO OTHER. (Deut 4:35 & Isaiah 45:5).

This one true God is revealed as the eternally self existent being who planned the whole of creation for inheritance by His HUMAN Son.

This human Son is Jesus. He is mentioned often, never as already existing, but always as one who is yet to be BORN. Significantly, He is THE MAN who will be the fulfillment of promises made by God to specific people, (Eve, Abraham, and David), about the future work of a direct descendant in their blood line.

Nowhere in the Old Testament is Jesus spoken of as a then existing personality. 

Nor is there any mention of Jesus as part of a "tri-une God". The concept of the Trinity is totally foreign to the Old Testament.

God is ONE, and God is self existent. God is NOT A MAN. Nor is He the Son of Man. 

Jesus, however, is not self existent. His existence is derived from God in fulfillment of promises made by God, that He would be both Son of God and Son of Man ...... and since God is neither of those things, Jesus therefore cannot be God. 

The distinct separate personalities of God and Jesus, the future existence and work of Jesus, and the subordinate nature of the relationship of Jesus to God, are all prophesied by David in Psalm 110 ..... "The LORD (Yahweh) said unto my lord (adoni), sit at my right hand until I make your enemies your footstool".

In this Psalm Jesus is NOT Yahweh. He is someone else. 

Yahweh, who alone is God, would speak to this other lord at some time in the future, issuing an invitation to assume the important, but definitely subordinate, role as God's chief deputy ...... the "right hand man".

JESUS AND THE GOD OF MOSES

Moses was not a Trinitarian!

The faith of Moses in one God only, (not three, or three-in-one) is expressed, clearly and unmistakably, in the Shema ..... "Hear O Israel: the LORD our God is one LORD; and you shall worship the LORD your God with all your heart, and with all your soul, and with all your might." (Deut 6:4)

Although Moses has much to say about Jesus, it is NEVER that Jesus is YAHWEH, the one LORD.

JESUS AND THE GOD OF CREATION

The faith of Moses in One God is older than Moses. It dates back to creation.

It is this One God who Moses wrote about as the the Creator of the heavens and the earth. (Genesis 1:1). 

He is the one who said "Let us make man in our image, after our likeness, ..... and let them have dominion ..... over all the earth." (Genesis 1:26).

It is sometimes claimed here, by Trinitarians, that the word, "us", reveals God as more than one . However this is not logical at all. Nor does it make any statement at all, about Jesus as a person then existing as part of a tri-une God. What it does tell us, is that God was speaking to others who were present. 

That there were others present when God laid the foundation of the earth, and the identity of those others, is revealed in Job 38:7. They are the "sons of God" ..... the angels. The God who speaks in Genesis, to those others, is the ONE who Moses declared to be God alone. In other writings of Moses it becomes clear that Jesus cannot be present at the creation, either as the speaker or a hearer. He is at the centre of the creation plan to make man, but not then personally in existence.

In this WORD, spoken at the beginning, the One True God declared his purpose to BECOME the Father of Jesus. 

Adam was only the starting point. It is Jesus who was the primary goal of God's plan in creation. It is the MAN, Jesus, for whom all creation was made by His Father . 

It is the MAN, Jesus, who bears the full image and likeness of the One God who is His Father. 

It is the MAN Jesus, who is the one through whom all other men will receive from God, the promised dominion over all the earth.

JESUS AND THE GOD OF ADAM AND EVE

Moses wrote about The One True God as the God of Adam and Eve. 

He is the God who created them and placed them under law to learn His likeness through obedience. 

When they tried to steal that impossible short cut to the likeness of God, and through disobedience, incurred the death penalty, the One True God became a Divine Saviour, by promising a future human saviour.

God's provision for their salvation would be a descendant of Eve, who would win the ultimate victory over sin. (Genesis 3:15). 

It is the MAN, Jesus, who became this descendant.

JESUS AND THE GOD OF ABRAHAM

Moses wrote that the One True God, who appeared to him at the burning bush, revealed Himself as the God of Abraham, Isaac and Jacob. (Ex 3:6). 

By this, He is identified as the God who made promises to Abraham which are the foundation of our own New Testament faith in Jesus.

The central theme of God's promises to Abraham, is the FUTURE "seed of Abraham", the Messiah, through whom they would be fulfilled. 

The God of Abraham is the one who promised that a descendant of Abraham would bless all families of the earth. It is the MAN, Jesus, who is that descendant, through whom all who share the faith of Abraham are blessed by being by turned from their sins. (Acts 3:25-26). 

The God of Abraham is the one who promised that Abraham and his descendant would inherit the earth as an everlasting possession. It is the MAN, Jesus, who is this promised descendant. It is through Jesus that all others who share the faith of Abraham also become his true spiritual heirs , and with Jesus, inherit that everlasting dominion over the earth.

JESUS AND THE GOD OF DAVID

This same One True God is the one who promised David that one of his descendants would sit on the throne of David for ever. 

To David, God also revealed that this FUTURE king, not yet born, (for how else could he be David's descendant) would also be GOD'S OWN SON (" I will be his father and he shall be my son ." (2 Samuel 7:14). 

In recognition of the promise that this future king would also be Son of God, David prophesied about him, calling him lord, (but NOT Yahweh). Thus he declared that his descendant would be subordinate to God, but superior to David.

It is Jesus, who is both Son of David and Son of God.

JESUS AND THE GOD OF ISAIAH

Isaiah speaks clearly of the distinction between the MAN, Jesus, and the God who stands alone.

For Isaiah, God is the LORD, the one who Moses declared to the One True God. There is no other. (ch. 43:10-14 & 44:8 & 45:5-7).

He is the God who speaks the word which will stand for ever. (ch. 40:8).

He is the LORD, (the Yahweh of Moses), who is the everlasting God, the creator of the ends of the earth. (ch. 41:28).

He is the God who promises the coming of the man who will be the future Saviour, Priest and King. (The Messiah).

Isaiah speaks often of Jesus. The word of God which stands for ever, is spoken about Jesus.

In Isaiah 9:6-7, Jesus is described as a future son of the Jewish race. This Jewish son is the one who will sit on David's throne, (and will therefore be the one promised as Son of David and also Son of God.) Because he will be the Son of God, he will bear the names and titles of God, which rightly also belong to a Son.

In Isaiah 53, Jesus is revealed as the MAN who would become the suffering Saviour, dying to bear the penalty for the sins of all who accept His sacrifice.

In this role He reveals the arm of the LORD, but is not himself the LORD. (v1).

As the sin bearer, upon whom the LORD has laid our iniquities, he is the LORD'S agent in our salvation, but is not himself the LORD. (v6).

As the man in whose hand the will of the LORD is to prosper, He is distinct and separate from God. (v10).

He is not God, but the servant of God. (v11).

And because of His victorious sacrificial role as the human AGENT of the Divine Saviour, he is to be highly exalted. (v11-12).

MESSIAH is a Hebrew word meaning "anointed". It is the direct equivalent of the Greek and English "Christ".

In Isaiah 61, Jesus is prophesied as the future Messiah, the LORD'S anointed one. The Lord GOD, (Yahweh, who is alone is God) will anoint Jesus for the work of salvation.

It is the anointing by the Spirit of God, which declares him to be God's MESSIAH. He is the promised human King and Priest after the order of Melchizedec, anointed for His role by the Spirit of God. As Messiah he is sent by God (v1). Since he is sent by God, he cannot himself be the One True God.

CONCLUSION

We have touched only a few of the major references, from a few writers of the Old Testament.

The other writers are uniformly agreed.

The LORD is God. The LORD alone is God.

Nowhere in the Old testament, is Jesus ever anything other than a FUTURE man, whose relationship to God will be that of a Son who is also a servant. The Son will be God's agent, but cannot himself be God, for God, though He may be a Father, is neither a man, nor the son of Man.

In all of these promises, God remains alone as the ONE TRUE GOD. 

Jesus is promised but not yet in existence. He is the FUTURE plan, THE WORD spoken by God, which is certain to come to pass.

But nowhere in the Old Testament is there the slightest hint that Jesus already exists as a person who is part of a tri-une God, or as a pre-existent spirit being. 

How, if he was either, could he ever be truly a man? It was a MAN who was promised, and if God is true to His word, then a REAL MAN Jesus must be.

Men who believe in the pre-existence of Jesus as God, may pay LIP SERVICE to His manhood. In that, without question, they may even be sincere. 

However, truth is the issue in question, not sincerity.

And that lip service to manhood is an abuse of language, a confusion, a lie, which says one thing, but in the same breath effectively denies it, by making of Jesus something that could never be really a man.

The God of the Old Testament will not share His glory with another. (Isaiah 42:8 & 48:11).

In the New Testament, He has not laid that glory aside, nor has he given it to another. 

However, He does now receive that glory which is His alone, from all who bow the knee to His glorified, but subservient, Son. (Phil 4:9-12 & 1 Cor 15:27-28).

This God is revealed to us by His Son, the man Christ Jesus, who is the Mediator between God and men. (1 Tim 2:5).

It is Jesus who acknowledges the One God of the Old Testament, as both His God and our God. (John 20:17).

And it is Jesus who repeats the words of Moses, commanding us to love this God as the LORD our God, with all our heart, and with all our soul, and with all our mind, and with all our strength. (Mark 12:29-30).