Why was Paul in prison when he wrote these three letters?

Les explains that Paul ended up in prison because of his apostleship, and it is from that imprisonment that he writes these next three letters. Before his conversion, Paul hated anything associated with the Christ of Calvary and thought he was destroying his pet religion, Judaism. But God in grace saved him on the road to Damascus and immediately gave instructions that he would go to the Gentiles with a whole new format—not based on Judaism, the Law, or the Old Testament, but on a new revelation of truths never before mooted. He was sent among pagan Gentiles and was constantly confronted with abject immorality, yet out of that wickedness he turned the Roman Empire upside down by simply preaching the Gospel. He was not a crusader, politician, or moralist, but preached the Gospel of the grace of God. Now, as he ends up in prison because of his apostleship, he writes these three letters. He is an apostle not by his own volition but by the will of God, and he writes to the saints—always to the believer, the Christian.