Galatians 1:1 is the Apostle Paul saying this about himself:
1 Paul, an apostle—[special messenger appointed and commissioned and sent out] not from [any body of] men nor by or through any man, but by and through Jesus Christ (the Messiah) and God the Father, Who raised Him from among the dead—
Notice that there was no group of people deciding that Paul (previously Saul) should be the new apostle! There were no lots cast or votes counted! The One, True God selected him! SO, because Paul was selected by God, did he just automatically know all the "deep" things that he taught? NO! Look at what he said in verses 15-18:
15 But when He, Who had chosen and set me apart [even] before I was born and had called me by His grace (His undeserved favor and blessing), saw fit and was pleased 16 To reveal (unveil, disclose) His Son within me so that I might proclaim Him among the Gentiles (the non-Jewish world) as the glad tidings (Gospel), immediately I did not confer with flesh and blood [did not consult or counsel with any frail human being or communicate with anyone]. 17 Nor did I [even] go up to Jerusalem to those who were apostles (special messengers of Christ) before I was, but I went away and retired into Arabia, and afterward I came back again to Damascus. 18 Then three years later, I did go up to Jerusalem to become [personally] acquainted with Cephas (Peter), and remained with him for fifteen days.
He didn't "magically" know so much and no human person taught him! How DID he learn so much then? At the feet of Jesus! He said that he did NOT confer with people! He spent time in the Word of God that he already knew as a well educated Hebrew, but the Holy Spirit taught Him what it all meant and how it relates to the church! I am convinced that even Paul did not completely understand everything that he taught, and WE are still learning aspects of the Word today! The Word of God is LIMITLESS and there is NO END to the wonderful things we can learn from it everyday that we ATTEND to it (Proverbs 4:20-22)! AMEN! Make THAT your determined purpose today! Here is Hillsong United with "Nova":
Shalom in Him!