From the introduction:
Although the gospels of the New Testament are among the most widely recognized and read documents in the world, it remains difficult to explain their exact genre. The gospels have no clear parallel in any other religious or literary tradition.
A Unique Form Of Writing
Certainly, the gospels are not mere biographies. They do not offer enough data about the life of Jesus to construct a full story of his existence, or to offer a well-developed social portrait of his presence among his contemporaries. While Matthew (1:18-2:23) and Luke (1:5-2:40) each related a few events surrounding Jesus' birth, their selections differ significantly from one another. Luke briefly told of a single incident in Jesus' early adolescence (2:41-52), and then jumped quickly to Jesus' baptism by John, indicating that this took place when Jesus "was about thirty years old" (2:23). The bulk of all four gospels proceed from this inaugurating event, bypassing almost entirely Jesus' first three decades of life. Since John included notes about Jesus participating in three Passover celebrations (2:13-25, 6:4, 13:1), the last of which became the occasion for his crucifixion, it is commonly assumed that Jesus was thirty-three years old when he died. But the gospels are certainly not clear, concise, or comprehensive biographies of Jesus' life.