I am not sure that you can be certain on this statement. You said in your post #787, "Paul certainly knew about predestination and election." While Paul certainly knew about predestination and election, he did not necessarily have a better understanding than we have today.
My wife and I memorized Ephesians about twenty years ago. At that time I did not pay much attention to "predestination." Likewise when I did Romans I didn't even notice "election." It is not until you are challenged on a particular point that you begin to pay attention.
Did Paul know that he was writing scripture? (I suspect he did) and if he did know, did he realize that he was writing way over his head?
Well, I would respectfully disagree because Paul wrote about predestination and election, and he was an inspired author of God. Therefore, I would give him credit for knowing more than any person around today on those subjects. As inspired, we consider Paul's writings "perfect" and not subject to being improved upon over the ages.
It is not until you are challenged on a particular point that you begin to pay attention.
Amen, and good for you and your wife for your memorization. I have memorized long passages before, but not a whole book. I agree with you that memorization, while always good, does not necessarily mean full comprehension. As I continue to learn today, I revisit old memorized passages and discover further meaning.
Did Paul know that he was writing scripture? (I suspect he did) and if he did know, did he realize that he was writing way over his head?
The first question is comparatively easy for me to address, and agree with you, that Paul knew he was writing scripture. Peter acknowledges that Paul's writings were scripture in 2 Pet. 3:14-16. So, if Peter knew ......
The second part was much harder for me and I went around and around about it. My conclusion was that to the extent that scriptures are comprehensible by man, Paul knew more about what he wrote than anyone since. He was an inspired author, and if Paul's own writings were above his head then who could have understood them? If no one, then the purpose of the Bible would be thwarted as the revealed word of God.
At the same time, I don't think Paul would have claimed to have had an equal understanding of all scriptures, for then he would have had no potential left for growth himself. But, I think this is OK, since the revelation to and the witness of each author in scripture is unique. Each author wrote what the author witnessed, either through experience or through revelation.