“When Jesus was teaching Paul, was he seeing Him, or how did he learn exactly?”
Paul answers this question when he wrote, “I will come to visions and revelations of the Lord” (2 Cor. 12:1). We know that “revelations” are the revealing of things that were kept secret, for Paul says he received “the revelation of the mystery, which was kept secret” (Rom. 16:25). Similarly, “The Revelation of Jesus Christ” (Rev. 1:1) is a book that reveals “the wrath of the Lamb” (Rev. 6:16) that was kept secret in the “meek” way the Lord lived on earth (Matt. 11:29; 21:5).
The writer of Revelation wrote, “I John…am your…companion in tribulation…and in the kingdom” (Rev. 1:9). Neither the tribulation nor the kingdom that John went on to describe had yet begun, but he was the “companion” of his readers in both those things, for he was with them “in the Spirit” (Rev. 1:10) in a virtual reality sort of way. That is, the Lord gave him a realistic vision of the future and told him to write down what he saw (Rev. 1:11,19).
In the same way, Paul says the Lord revealed the mystery to him by revelation (Gal. 1:12) and said that He would continue to reveal it in more “visions” (2 Cor. 12:1). He then went on to describe one of those visions (2 Cor. 12:2-4), one that seemed so real he couldn’t tell if he was “in the body, or out of the body” when it happened (2 Cor. 12:3).
But we know that this is how the Lord revealed the mystery to Paul, for he says that in that vision he “heard unspeakable words, which it is not lawful for a man to utter” (2 Cor. 12:4). Those were words that had to do with the mystery, words of grace that weren’t lawful to speak under the law, such as the reversal of the diet laws of Leviticus 11 in 1 Timothy 4:4,5. source