This is a defense that I should have given eight years ago in my Old Testament class at the University of Louisville. I didn’t have a defense then, but now I have an answer.
Gen 1.26-27 which says:
Then God said, “Let us make man in our image, after our likeness. And let them have dominion over the fish of the sea and over the birds of the heavens and over the livestock and over all the earth and over every creeping thing that creeps on the earth.” So God created man in his own image, in the image of God he created him; male and female he created them. The problem arose when the professor said that when God said, “Let us…” he was not referring to himself in the plural. That is, there is no shadow of Trinity in the Old Testament. He said it was just a poetic form of majesty. When kings spoke they used the plural. Nevermind this was an assertion not pointed out in the Bible at all. He also said it could be that God was speaking to the angels. I read a paragraph in Anthony Hoekema’s book, Created in God’s Image, that I wish I had read eight years ago:
Some [scholars] call it a ‘plural of majesty,’ an unlikely possibility since such a plural is not found elsewhere in Scripture. Others have suggested that God is here addressing the angels. We must also reject this interpretation, since God is never said to take counsel with angels, who -themselves creatures – cannot create man, and since man is not made in the likeness of angels. Rather, we should interpret the plural as indicating that God does not exist as a solitary being, but as a being in fellowship with ‘others’ (p. 12).
Read ‘em and weep, Professor! Read ‘em and weep.
Though we cannot conclude that this is a clear teaching of Trinity in the Old Testament, we have to at least understand the Bible as speaking of God as One yet existing in relationship. God’s revelation in Scripture is historically progressive. We have the seed of the Old Testament coming to fruition in the New Testament (as Geerhardus Vos explains). In other words, Gen 1.26-27 is preparing people for the fact that God exists as One Being in Three Persons. To teach this without giving some kind of shadow and paradigm in which to think of God would shock and propel someone into disbelief.