Whether for Christians, Jews, or other non-Catholics, no understanding of a World Religion with over one billion members can be approached without some knowledge of St. Paul.  An excellent book to assist in this study is "In Search Of Paul", by John Dominic Crossan and Jonathan L. Reed (Harper San Francisco, 2004).  The following are a few insights from that book.

• Saul was a fervent Jew who was greatly troubled when he came to be persecuted as much by the Jews, who opposed his evangelizing among the gentiles and among pagan sympathizers of the Jews, as by the Romans.
• The Caesars opposed him because the foundation of their power was their claim to be God, Son of God, God of God, Lord, Redeemer and Savior of the World (px).  Paul presented another claimant to those titles, the one and only, Jesus Christ.
• The ancient Jewish religion was very strong and resourceful, and was generally tolerated by Rome.  The new religion that Paul spread throughout the Mediterranean basin was directly opposed to Rome's Imperial theory, while it targeted the pagan God-worshipers in the Jewish synagogues for their allegiance.   Any wonder then, that Paul lived a dangerous and exciting life?
• And if that wasn't enough, Paul had to deal, both during life and after death, with objections to his vision of Jesus' teachings.  His was a Christianity of inclusion, of willing Jews, of gentiles (without need for circumcision), and of women.  All were to be welcome, and all were equal.  After his martyrdom in Rome, probably with St. Peter, some of the Letters attributed to Paul were actually written by others (the so-called Lukan Paul), with different teachings or at least different emphases.  Some of the original Apostles, those who actually had lived with Jesus, even tried to withhold from Paul the honor of "Apostle", always treasured - rightly - by this other foundation-stone of the Catholic Church.
• Ultimately, the message that St. Paul the Apostle brought from Jesus' teachings to His Church was a vision, not of "Violence, and then Peace" which had been the unsuccessful modus operandi for eons...but of "Justice, and then Peace", something that we all still aspire to.

"When I came to you, brothers and sisters, proclaiming the mystery of God, I did not come with sublimity of words or of wisdom.  For I resolved to know nothing while I was with you except Jesus Christ, and him crucified.  I came to you in weakness and fear and much trembling, and my message and my proclamation were not with persuasive words of wisdom, but with a demonstration of Spirit and power, so that your faith might rest not on human wisdom but on the power of God."

GS