We think of the concept of the Trinity, the Father, Son and Holy Spirit, as belonging to the New Testament. Of course, we know that the Trinity has existed always. We find that the Spirit of God hovered over the waters in Genesis 1:2. And we know that God the Father is found throughout the Old Testament.
We know this entity as God the Father, but to the Jews He is God - period. They do not have the concept of the Trinity. They especially do not believe in the idea of God the Son. It is not found frequently in the Old Testament, but the prophet Isaiah calls our Heavenly Father, Father specifically, in Isaiah 63:16.
The Holy Spirit is found several places in the Old Testament. The phrase “Spirit of God” occurs at least twenty times in the Old Testament alone. In Egypt, Pharaoh found that Joseph had the Spirit of God. (Genesis 41:38) In Judges, both Jephthah and Samson had occasions where the Spirit of God came over them and gave them victory. The Holy Spirit entered Saul in First Samuel chapter ten. Again, the Jews view this as the spirit of God, rather than a separate entity.
There is not much direct mention of God the Son in the Old Testament. It is frequently pointed out in that Genesis 1:26 God says “let us create man in our image.” The word us indicates unity, according to Strong’s Concordance. But this implication does not specifically note God the Son.
My favorite is found in Proverbs 30:4. In this proverb of Agur, he asks, “Who hath gathered the wind in his fists?” “Who hath established all the ends of the earth?” “What is his name, and what is his son's name?” To Christians it is quite obvious. We know Who has these powers; God the Father. But Agur asks, “And what is his son’s name?” In the Old Testament, in Proverbs 30:4, the writer asks for the name of the Son of God. So all three entities of the Trinity are specifically mentioned or referred to in the Old Testament.
According to Brother Jacov Rambsel, a born-again Christian who was ethnically a Jew, the Lord answers the question in Proverbs 30:4. Brother Rambsel, who reads Hebrew, has discovered within the text of this verse the answer to “and what is his son’s name?” In letters equally spaced within the text of Proverbs 30:4, he found the name Jeshua. This is the Hebrew version of the Greek name, Jesus.
The Holy Trinity, including Jesus the Son, is found in the Old Testament. I am not surprised. Praise the Name of the Lord; and praise the Name above all names, Jesus.