Catechism of the Catholic Church

We can distinguish three stages in the formation of the Gospels: (76) The life and teaching of Jesus. The Church holds firmly that the four Gospels, "whose historicity she unhesitatingly affirms, faithfully hand on what Jesus, the Son of God, while he lived among men, really did and taught for their eternal salvation, until the day when he was taken up." The oral tradition. "For, after the ascension of the Lord, the apostles handed on to their hearers what he had said and done, but with that fuller understanding which they, instructed by the glorious events of Christ and enlightened by the Spirit of truth, now enjoyed." The written Gospels. "The sacred authors, in writing the four Gospels, selected certain of the many elements which had been handed on, either orally or already in written form; others they synthesized or explained with an eye to the situation of the churches, while sustaining the form of preaching, but always in such a fashion that they have told us the honest truth about Jesus."