From the beginning the churches took care to preserve the letters they received from the Apostles, since in them they had authoritative witnesses to the faith. It was more difficult then than it is today to gather these documents, and even save the perishable material of papyrus from dampness.
Before long, there was an initial collection of the first seven epistles arranged in the order of decreasing length: the four “great” letters to the Romans, to the Corinthians and to the Galatians, and “the letters from captivity”. Others came to be added: first, those to the Thessalonians which are actually the oldest; and then those that were passed on under the patronage of Paul: the letters to Timothy and Titus which were written some twenty or thirty years later, and the beautiful letter to the Hebrews, written most likely under the influence of Paul but by an unknown author. A phrase from the “second letter of Peter” (not written by himself but about fifty years after his death) is evidence that from this time the letters of Paul were counted among the inspired Writings (2 P 3:15-16).
Paul saw himself as “the apostle to the pagan nations”, seeing there his personal vocation beside Peter (to whom God had confided the charge of evangelizing the Jewish world) not only in Palestine, but also throughout the Roman Empire, wherever they were established. Paul received this mission from Jesus himself at the time of his conversion (Acts 22:21; Gal 2:7); so highly fundamental was it in the divine project of the mission and extension of the Church that it remained unfinished at the time of his death. The spirit of Paul, one of the great manifestations of the spirit of Jesus, is always at work in our midst through his letters.