What books do we consider to be scripture?
The books that the councils of the 2nd and 3rd centuries held to be scripture. Note that the Ethiopian church has the most number of books in scripture - 84.
The author of the Pauline epistles is, well, Paul who was inspired by God. Paul wrote as a human inspired by God.
The author of the passages in the Old Testament that testify of Christ - whether Moses or Ezekiel or Isaiah or Daniel didn’t KNOW Christ as we know Him, they knew Him as the Word of God, as God in short.
Proverbs 25:2 It is the glory of God to conceal a thing: but the honour of kings is to search out a matter.When you find something concealed in scripture, it is more likely that God put it there and not men. How common is that? In fact the men that recorded God’s inspired word likely did not know or understand many of the things they were writing. I wonder if Paul studied his letters as we do since he knew he was writing scripture.