Catholics believe that the gospels were written at the end of a three-stage process.
Stage 1: The Life and Teaching of Jesus. This period lasted from the birth of Jesus around 4-6 BC to his death around AD 30 or 33. It includes what Jesus did and taught. Preeminent in each gospel is testimony about Jesus’ death and resurrection. The Church teaches that the gospels faithfully hand on what the historical Jesus did and taught for our eternal salvation.
Stage 2: Oral Preaching about Jesus. This period lasted from the founding of the Church on Pentecost Sunday until the gospels were written. During this time the apostles reflected on the meaning of Jesus and God’s work through him. They used hymns, catechetical lessons, prayers, stories, testimonies, and the like to present the words and deeds of Jesus. Some of the traditions about Jesus probably began to take written form during these years.
Stage 3: Written Gospels. The different gospels were written over a period of about 35 years. Mark wrote around AD 65, Luke and Matthew between AD 75 and 85, and John in the last decade of the first century. Each evangelist adapted his materials keeping in mind the circumstances of the particular audience for whom he was writing. Thus, we have four versions of the gospel (“good news”) because each of the evangelists was writing for a different community of Christians (for example, Gentiles or Jewish converts) in different circumstances.