OK, maybe not exactly the trinity. But that God is ONE God and that God is made up of at least 2 "persons" is taught for sure, the trinity is either taught or hinted at.
Genesis 1: "God said let US make man in OUR image"
According to a friend of mine, a Jewish Rabbi, The word God in the Hebrew text is singular, the words US and OUR are plural.
So, though my Rabbi friend says "Yeah, but we reject the idea that God has multiple persons, we think that God was simply speaking metaphorically when he said let us make man in our image" he DOES agree that IF God has multiple persons and IF Jesus is part of God, then this verse in Genesis would have to be interpreted literally rather than figuratively.
Gen 3:23 "as one of us" re-emphasizes
Deut 6:4 "Hear, O Isreal! The Lord is our God, the Lord is One." I'm still thinking about this one, clearly it tells us that there is only one God, but it may imply that hes parts are bound as one.
Isaiah 6:8 "who will go for us"
Since we started with "Jesus is God" in our first lesson, we can clearly see that the Old Testament started right off the bat with the assumption that God had multiple persons. That Moses understood that and simply accepted it. It is men who have chosen to change the meaning.
Psalm (110 I think) "The Lord said to my lord". Two different Hebrew words for lord here. The Jew accept that the first is God (Yaweh) what we call God the Father, and that the second one was the Messiah. The second two parts of the trinity.
Is the Messiah God? Yes. Only God can give life:
Deut 32: 15,18 He abandoned the God who made him and rejected the Rock his Savior....You deserted the Rock, who fathered you; you forgot the God who gave you birth. (Savior = Messiah).
Jesus asked how can David say this. Because it suggests that the Messiah - which the Jews understood would be a descendant of David WAS ALREADY ALIVE and God was talking to him. This verse tells us that the Messiah was(is) alive before he was(will be) born. He would have to be God for this to be true AND God would have to have multiple persons since "God the father SAID TO God the Messiah." Note that Jesus teaches here that we should treat the scriptures literally.
Is the Holy Spirit part of the trinity?
Gen 1:2 "Spirit of God" hints at the third member of the trinity. However, it is fair to say that this might not have been an "obvious" translation until later.
The following don't "prove" the Holy Spirit is part of God, rather they show the work of the Holy Spirit prior to the time of Christ:
Isaiah 11: 1-2 (to be fair, this may be talking about what the Spirit will do in our future still)
Jeremiah 31:33-34 - I will write my law on their heart
Ezekiel 36:26-27 - I will give them a new spirit. I will put my spirit within them.
But is God one?
Yes that is very clear too. Deut 6:4- 6.
Isn't this a hard concept? One God but multiple persons?
Yup. That's why so many people reject the teaching of the trinity (or at least duality) in the Old Testament, but it doesn't change the fact that the OT teaches that God had multiple persons, 2 and possibly 3.
End of Lesson.
OK, but let me give an illustration.
What is Water? Is there more than one element "Water?" No. H2O is H2O is H2O. If it isn't H2O it isn't water!
But Water can be a solid, liquid or Gas.
Here is where it becomes fun.
What do we call the three parts?
Solid, we call "ICE" or "Solid Water" or "Snow"
Gas, we call "Steam" or "Vapor" or "Clouds" or "Fog" or "Water Vapor"
Liquid we call "Water" or Liquid Water.
If someone says to you "Water" without any qualifications. They are either talking about all three states (where the state is irrelevant) as in "there is lots of water on earth. It is in the oceans, in icebergs and in the air" OR they are talking about the liquid specifically.
In the same way, when we say "God" we are either talking about God in any of his three persons, or we are talking about God the Father.
Consider this Chart:
"Water" is equivalent to "God". "God" = "God the Father" or "God in general"
"Ice" is equivalent to "Jesus". "Jesus" = "God the Son"
"Steam" is equivalent to "Holy Sprit". "Holy Spirit" = "God the Hold Spirit/Ghost"