A 19th century picture of Paul of Tarsus

Paul of Tarsus (originally Saul of Tarsus) or Saint Paul the Apostle (fl. 1st century AD) is considered by many Christians to be the most important disciple of Jesus, and next to Jesus the most important figure in the development of Christianity. The Apostle Paul himself was a Jew from Greece of that time (Tarsus of present-day Turkey), and it was he who first made great efforts in his epistles to the Romans in showing that God is for all the people, not only for Jews. As for a good-hearted divinity, the Greek philosophers prepared people for it.

Paul is recognized by many Catholics and all Eastern Orthodox Christians as a saint. Paul did much to advance Christianity among the gentiles, and is considered one of the primary sources of early Church doctrine. His Epistles form a fundamental section of the New Testament. Some argue that it was he who first truly made Christianity a new religion, rather than a sect of Judaism.

Due to this body of work and his undoubted influence on the development of Christianity, many modern scholars have considered him the secondary founder of Christianity, modifying Jesus' teachings and adding important new doctrines. However, this view remains controversial. For example, conservative Christian scholars say that no teachings were modified; rather, Paul elaborated in complete harmony with Jesus.

His theology

Paul had several major impacts on the nature of the Christian religion. First was the concept that the death and resurrection of Jesus superseded the value of the Mosaic Law, a belief that is often expressed as "Jesus died for our sins." It is unclear how much of this idea is original with Paul; Jerome notes the existence in the 4th century of a heretical Christian sect in Syria called the Ebionites who still observed the Mosaic Law, thus suggesting at least some Christians may not have believed in the salvatory qualities of the Passion.

However, there is some evidence that suggests Paul's concept of salvation coming from the death of Jesus was not unique amongst Christians; Phil. 2:5-11 which expounds a Christology similar to Paul's, has long been identified as a hymn of the early Christians, and dated as existing before Paul's letter.

Related to Paul's interpretation of the resurrection are his concepts of faith, which he explains through his explanation of Abraham, and of righteousness and the forgiveness for sins, using language that Augustine of Hippo later elaborated on in his formulation of original sin.

In the New Testament the doctrine of original sin is most clearly expressed by Paul's writings. His writings also clearly express the doctrine that salvation is not achieved by conforming to Mosaic law, but through faith in (or faith of) Jesus Christ. This doctrine was confirmed at the Apostolic Council (see above). Paul was also one of the first Christians to expound the doctrine of Christ's divinity.

One development clearly not original with Paul, but for which he became the chief advocate, was the conversion of non-Jews to Christianity. While a number of passages in the gospels (e.g. Mark) begrudgingly acknowledge that Gentiles might enjoy the benefits of Jesus, Paul is known as "The Apostle to the Gentiles", a title that can be traced back to Gal.2:8. His missionary work amongst the non-Jews helped to raise Christianity to more than a dissident—if not heretical—Jewish sect.

Paul also develops a strong doctrine of the Holy Spirit. Much of Romans and particularly the ending to 2 Corinthians portrays the Spirit in equality to the Father and Son. These inferences would later be developed into the doctrine of the Trinity. Paul's notion that the Holy Spirit dwells in all believers at the time of their conversion is integral to his soteriology, ecclesiology, missiology, and eschatology.

His social views that became part of Christian doctrine

Paul's writings on social issues were just as influential on the life and beliefs of the Christian culture ever since as were his doctrinal statements. In fact, being part of the texts that were generally accepted as inspired scripture, these views were and still are considered part and parcel of the broader Christian doctrine by the more conservative Christians.

Paul condemned sexual immorality, homosexuality in particular, apparently based on the strict moral laws of the Old Testament, as well as presumably his own private revelation from the Holy Spirit (1 Cor. 6:9f; Eph. 5:21-33). (Paul is traditionally considered a virgin.) Some of his other dictums included advice to his contemporaries not to marry in the expectation of the near return of Jesus and the Apocalypse; permission to marry, or at least to stay married to, an unbeliever, in the hope that the spouse of a Christian will be converted sooner or later; the recommendation for women to obey men (based on the story of Eve—"man was not made for woman, but woman was made for man") and raise families; the "he who does not work, neither shall he eat" dictum; and the command to young men who have trespassed by sleeping with a woman to marry her, a notion that remained prominent in the European culture and the English Common Law until relatively recently.

Paul may have been ambivalent towards slavery, saying that pending the near return of Jesus, people should focus on their faith and not on their social status (1 Cor. 7:21f). Due to his authority, these views have had an influence in Western society into modern times; Paul's failure to explicitly condemn slavery in his Epistle to Philemon may have been sometimes interpreted as justifying the ownership of human beings.