But it was authored by mortals. Divinely inspired, yes, but properly speaking, authorship of the Torah belongs to Moses (or the sources of those traditions), inspired by God. It is still the voice of the author conveying Truth, but in a setting dictated by the milieu of the temporal author. Hence, there are two different creation stories at the beginning of Genesis, coming from two different sources, from two different eras, the priestly and the Yahwist. God wasn't being schizophrenic, He inspired two authors of differing backgrounds to present an entire picture.
Still, the reference of "the Rock" in the O.T. does not pertain to a direct quote from God, whereas "I AM", "thou art Peter", "Israel shall be thy name" and "thou shalt be called Abraham" are indeed directly attributed to the utterance of God. The authors of the O.T., who describe God as "the Rock" are conveying, in terms understandable to their audience, the everlasting, ever-powerful nature of God. It's a description, not a proper naming. This doesn't mean it's a false description - by no means, it's most definitely true! But the action of Jesus naming Simon bar-Jonah "Rock" is indeed a unique, creative event BECAUSE it came from the mouth of the Word made flesh, not the inspired reflections of the author.
Oh and Jesus Christ is the living Word of God from the beginning (John 1:1). Everything that was made was made by Him and for Him (John 1, Col 1, Rev) He didn’t only begin speaking to man when He was enfleshed.
How does this relate to the fact that nowhere does God directly state, "I am the Rock", but He does directly say, "Thou art Peter"? The whole of Creation is "And God said..." over and over again. When He speaks, there is Wisdom and Love, and through this Love, Creation. It's also no small detail that God gave to man the job of naming everything around him. To give name to something is to exercise dominion over it. When, instead of man, God gives name to something, that "something" directly and explicitly becomes the cherished possession of God - be it Abraham (father of nations), Israel (the Chosen), Jesus (the Savior), or Peter (the Church). God didn't hand out new names unless something extraordinary and new was being created at His own utterance. Since we cannot find anywhere in Scripture that God the Father names Himself (but to say 'I AM'), it stands that the naming of Simon bar-Jonah as "Rock" is a moment of Creation which cannot be paralleled by the words used by O.T. authors to describe God (not name Him, since God cannot be named by mere mortals who can never have dominion over Him).
You also might want to reread the Torah and the entire Tanakh for that matter. God spoke to Moses.
Yes. And He told Him his name - "I AM". He didn't say, "My name is up to you to decide." Thus, not being empowered to "name" God, the O.T. authors used descriptive appellation instead. (In similar fashion, man was not entitled to see the Lord God face-to-face because we can neither withstand nor contemplate the essence of God in our fallen natures. As such, the Lord condescended to be visible as a pillar of cloud, or as an "angel of the Lord". Yet no one would suppose that God's essence is properly just a cloud or angelic.) God, on the other hand, does have the authority to take possession of anything He chooses, be it a tribal leader (Abraham), a leader of tribes (Jacob), the His own Word made flesh (Jesus), or the preeminent shepherd of His flock, upon whom He promised to build His Church (Peter).