Rome, Italy—Outside the Basilica San Paolo Fuori le Mura, commonly known as the Basilica of Saint Paul, stands an imposing marble statue of a man who appears ready to do battle with the world. Bearded and hooded, he clutches a Bible in his left hand and a long cross in his right—but holds the cross over his chest as if it were a sword. It is a fitting representation of the man whose writings arguably have done more to rout the forces of bigotry and tyranny than those of any other figure in history.

Saul of Tarsus, an observant Jew who was renamed Paul after his dramatic conversion to Christianity, claimed a divine calling to bring the message of Jesus to those outside the Jewish faith, that is, to the Gentiles. His mission ended here when, according to tradition, he was executed by the authorities of Rome. Hence, the historical irony: Paul’s letter to the believers in Rome, the theological loadstar of the Christian church, helped to topple the regime that could not tolerate his uncompromising message of redemption.

A relentless evangelist with almost reckless courage, Paul is the dominant figure in the early decades of the Christian movement. Of the 27 documents that compose the New Testament, 21 are letters; 13 of them are attributed to Paul. His Letter to the Romans stands apart. Written around 57 a.d., near the end of his career, it contains the most thorough exposition of Christian doctrine in the Bible. It also advances concepts considered utterly radical for their time—ideas that would shape the course of Western civilization and the American political order.