The Apostle Paul had a greater understanding of who Jesus was than many of His disciples who walked with Him in the earth. It was better for Jesus to leave earth because many in His inner circle could not see or know Him beyond His humanity. The Holy Ghost was sent so that the TRUE Jesus could be revealed. Jesus said "He (The Holy Ghost) will take of mine and show it unto you" (John 16:15b). John saw it also--the book of Revelation is the evidence.
The reason why Paul received so much revelation of the Gospel and was able to explain it so well throughout roughly two-thirds of the New Testament is because he developed a total dependency on the Holy Spirit for his doctrine. Even though he was well-versed in the law and could have relied solely on his intellect, he did not. He said "I thank my God I pray with tongues more than you all" (1Cor. 14:18). The revelation came through countless hours in prayer. So much so that a messenger from hell was sent by satan to stop him in his tracks. Paul pursued the things of God with the same fervor that he persecuted Christians while he was Saul of Tarsus.
Paul writes in Galatians 1:15-17:
But when it pleased God, who separated me from my mother's womb, and called me by his grace, to reveal his Son in me, that I might preach him among the heathen; immediately I conferred not with flesh and blood: neither went I up to Jerusalem to them which were apostles before me; but I went into Arabia, and returned again unto Damascus.
As far as we know, Paul never knew Jesus on a personal level while Jesus was in the earth. However, by the Holy Spirit, he got to know Him really well. That is a great example for us to follow. We cannot expect to receive revelation any other way except through close fellowship and communion with the Holy Spirit. He desires to teach us one on one. He brings us the faith that we are expected to live by, and the love that empowers it (Jude 20-21). We no longer live the old life; the old man is dead. The new man now reigns in life with Christ.
Wherefore henceforth know we no man after the flesh: yea, though we have known Christ after the flesh, yet now henceforth know we him no more.Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new. [2 Cor. 5:16-17]
