Today’s post, as well as several posts to come, are excerpts from my new book, Can We Trust the Gospels? Investigating the Reliability of Matthew, Mark, Luke, and John.
If there’s one thing that all New Testament scholars agree on, it’s the fact that the Gospels were not written merely for reasons of historical curiosity. The most liberal critic and the most conservative commentator, and everyone in between, would surely agree that Matthew, Mark, Luke, and John were not writing simply out of antiquarian interest. They weren’t scholars who found Jesus fascinating and decided to write about his life to further their careers. Rather, they were faithful believers in Jesus who composed narratives of his ministry for theological reasons. In the language of our contentious world, the Gospel writers had an agenda. They were writing theology, not raw history (as if there were such a thing).
None of the evangelists had a hidden agenda, however. Each writer revealed quite plainly his theological inclination as well as his personal faith in Jesus. Matthew begins his narrative by referring to Jesus as “the Messiah, the son of David, the son of Abraham” (1:1). Not exactly the vocabulary of a neutral observer! Similarly, Mark starts his Gospel in this way: “The beginning of the good news of Jesus Christ, the Son of God” (1:1). Mark is telling a story he believes to be “good news,” and it concerns Jesus, whom Mark believes to be the “Christ” and “the Son of God.” (By the way, Mark speaks of the beginning of the “good news,” which in Greek is euangelion, or “Gospel.” This is probably the origin of the use of “Gospel” as the genre for the four biblical biographies of Jesus. Mark himself probably didn’t use “Gospel” in this way, however, but rather as a summary of the content of his biographical narrative. English translations that use “Gospel” in Mark 1:1 run the risk of missing Mark’s meaning.)
Luke is even clearer about the purpose of his narrative. In an introduction reminiscent of the secular historians who may have inspired Luke, he begins:

Since many have undertaken to set down an orderly account of the events that have been fulfilled among us, just as they were handed on to us by those who from the beginning were eyewitnesses and servants of the word, I too decided, after investigating everything carefully from the very first, to write an orderly account for you, most excellent Theophilus, so that you may know the truth concerning the things about which you have been instructed (Luke 1:1–4).

Luke is writing an orderly account of the events concerning Jesus so that Luke’s reader might “know the truth” about faith in Christ. More literally, Luke is claiming to help his reader have “certainty” about the one in whom he believes. This is not academic history so much as intentional discipleship. It is teaching meant to help a believer grow in his faith.
The purpose of the fourth Gospel is also plainly stated, though near the end of the book rather than at its beginning:

Now Jesus did many other signs in the presence of his disciples, which are not written in this book. But these are written so that you may come to believe that Jesus is the Messiah, the Son of God, and that through believing you may have life in his name (John 20:30–31).

According to this translation (NRSV), John’s primary purpose is evangelistic. He wrote “so that you may come to believe that Jesus is the Messiah, the Son of God.” The Gospel of John may in fact be the first evangelistic tract in human history. The fourth Gospel, like the Synoptics, has an openly stated theological agenda.
What I’ve said about the intentions of the Gospel writers is confirmed by the Gospels themselves. In the way they are structured, in the emphases of the stories, in the presentation of miracles, and in the stunning conclusion on Easter and thereafter, Matthew, Mark, Luke, and John show their theological purposes. The Gospels are, without a doubt, theologically motivated writings, composed for pastoral, evangelistic, or apologetic purposes, or some combination of the three.