The New Revised Standard Version of the Bible states: "Paul's letters are the oldest Christian documents we have. The first of them was written within 25 years of Jesus' death, and the last may have been written before any of the gospels." It lists the following letters in the New Testament as Paul's: Romans, 1 and 2 Corinthians, Galatians, Ephesians, Philippians, Colossians, 1 and 2 Thessalonians, 1 and 2 Timothy, Titus, and Philemon.
The order of these letters in the New Testament is based on their length not on their date — from the longest to the shortest. This may be because the letters are not dated and do not always contain evidence of the time they were written. Romans is the longest letter and Philemon is shortest letter of Paul in the New Testament. Paul may have written other letters, but these are the letters that the church had and chose to include in its new scripture.
In the letters of Paul we find the apostle to the Gentiles defending four teachings over against the Jewish Christian leadership of the church in Jerusalem. First, Paul asserts that the Jewish law is not necessary for salvation. Moreover, the pursuit of perfection through the law, he believes, is doomed to failure. Therefore, he preaches that we can only be saved by the grace of God through faith.
Second, Paul argues that the most important spiritual gifts are those that build up the church, namely teaching and preaching, and especially love for others. The gift of love is also Paul's way of summarizing Jewish law. The law of love, according to Paul, is the will of God, which we know in Jesus Christ.
Third, Paul affirms that salvation is in Christ Jesus alone. Paul argues that the Son of the Father is the Lord, who has been given all authority by the Father. The Spirit of God, Paul teaches, is united with God in Christ Jesus. Therefore, Paul proclaims there is one Lord, one faith, one baptism, and one church.
Fourth, Paul asserts that the promise of the gospel is resurrection from the dead with new, spiritual bodies, to live in the kingdom of God under the eternal rule of the Lord Jesus Christ. The kingdom has not yet come, Paul believes, but is coming soon with the day of the Lord. He warns that those who hope to be saved must stay alert and live with faith.
These teachings of Paul about faith, love, Jesus Christ, and the resurrection from the dead will appear over and over again in the gospel accounts of the New Testament. Paul's free interpretation of the Jewish scriptures will also be confirmed by the gospel accounts. Finally, as the gospels are clearly written for Gentile as well as Jewish Christians, we should not be surprised to find that they generally affirm the witness of Paul.