What did Paul see and hear when he was caught up into paradise?

Paul saw the glories of heaven and heard magnificent things when caught up into paradise. He heard unspeakable words that were not permitted or lawful for a man to utter. God allowed him to see and hear these things but instructed him to keep them to himself.

Les explains that Paul had a full exposure to heaven as we normally think of it, with all its beauty and no doubt its music. He saw the glories, he heard the magnificent things, and he was caught up into paradise, where he heard unspeakable words which it is not permitted or lawful for a man to utter. In other words, God told Paul, "I'm letting you see and hear, but you can't repeat it. You have to keep it to yourself." Paul then says he would not glory in himself but in his infirmities, not wanting any man to think of him above what he is seen to be or heard to be.

2 Corinthians 12:2

I knew a man in Christ above fourteen years ago, (whether in the body, I cannot tell; or whether out of the body, I cannot tell: God knoweth;) such an one caught up to the third heaven.

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Why was Paul not allowed to tell what he saw and heard in paradise?

Paul was not allowed to repeat what he saw and heard because God permitted him to see and hear but told him he could not repeat it and had to keep it to himself. Scripture says the words were unspeakable and not lawful for a man to utter.