Paul's letters are the earliest writings of the church in the New Testament.
The letters of Paul reveal how freely he interpreted the Jewish scriptures in order to make sense of his experience of the risen Christ. Paul sees his ministry to the Gentiles as the fulfillment of the scriptures of his Israelite ancestors, but he is well aware that many other Jews do not share his interpretation of the Jewish scriptures. His letters confirm that the leaders of the church in Jerusalem, the former disciples of Jesus, opposed Paul's attack on Jewish law.
Because Paul's ministry follows the death of Jesus, we tend to read the New Testament as though Paul wrote his letters after the gospels were written. If this were so, however, surely Paul would have referred to the New Testament gospels, because they often support his arguments with the leaders of the church in Jerusalem. Because Paul does not refer to the gospels, we can only conclude that they were written after he was put to death in Rome prior to the Jewish revolt in Jerusalem in 66 A.D.
We know that Paul began his ministry about three years after the church was
founded in Jerusalem, when he met Peter and James, the brother of Jesus who
became the leading apostle of the Jerusalem church. (Gal. 1:13-24) In
conversations with these apostles, who knew Jesus intimately 
during his life,
Paul must have heard stories about the teachings of Jesus and the events that
led to his crucifixion at the hands of the Roman authorities. Yet, in his
letters Paul says very little about the life and ministry of Jesus. Paul
preaches Christ crucified and raised from the dead, as the first fruit of the
resurrection of all the faithful. He does not tell the parables of Jesus found
in the first three gospels, and he does not draw on the teachings of Jesus in
the gospel of John.
Paul's letters are the written documents in the New Testament that are closest to the historical Jesus and the origins of the church, but they do not include a biography of Jesus or a history of the church. The letters of Paul were written to address problems in congregations and to persuade Christians of Paul's mission to the Gentiles. But Paul's letters allow us to see that the former disciples and family of Jesus, who form the leadership of the Jerusalem church, kept Jewish laws and expected other Jewish Christians to do so. The clear implication is that Jesus did not in his lifetime reject all Jewish law, even if at times he challenged those who were hypocritical in demanding strict observance.
Jesus was a Jew who understood himself and his mission in terms of the Jewish scriptures — the Torah, the Prophets, and the Writings. Paul also was a Jew, and he read the same scriptures, although in Greek. But Paul argued that "Christ is the end of the law and brings righteousness for everyone who has faith." (Rm. 10:4) Later, two of the gospels in the New Testament (Mark and Luke) supported his position. But preaching this gospel message in Gentile and Jewish churches led to an attack on Paul during his last visit to Jerusalem and set in motion his arrest, trial and imprisonment. (Acts 21:17-28:31)
To read more about Paul's letters.
