Redaction criticism asks why an evangelist altered his sources. To answer this, readers first identify the changes. For example, in the baptism of Jesus, Matthew and Luke both use Mark but edit it differently. The differences between Matthew and Luke reveal the concerns of their respective communities and their theological perspectives. In other words, Matthew and Luke are not mere compilers of earlier material but redactors — theologians shaping the tradition for their communities.
Why does Matthew insist on explaining the need for Jesus’ baptism by water? What was happening in Matthew’s community, and what theology is he promoting?
Two plausible concerns in the Matthean community are:
1) Why would Jesus submit to John’s baptism if John’s baptism is for the forgiveness of sins?
2) Does Jesus’ authority appear inferior to John’s because Jesus was baptized by him?
Matthew’s answer is succinct: Jesus’ baptism is required “to fulfill all righteousness,” a recurrent Matthean theme rooted in the Hebrew Scriptures. In Matthew’s presentation, baptism signifies surrender to God, the inauguration of Jesus’ public ministry, and a commitment to enact God’s justice. Thus, Jesus’ baptism is not about repentance and forgiveness in the ordinary sense, nor does it imply that his authority is subordinate to John’s.
The conversational, explanatory style of Matthew’s baptism narrative fits the Gospel’s broader didactic character; Matthew frequently supplies interpretive material (e.g., the Sermon on the Mount, extensive teaching cycles) to clarify theological and ethical points for his community.
Why does Luke emphasize the crowd’s presence at the baptism and Jesus’ prayer? This reflects Luke’s pastoral, “down-to-earth” concern with the public and social dimensions of Jesus’ ministry, and his consistent interest in prayer. As for why Luke omits some of Mark’s baptismal details, we cannot be certain. One reasonable possibility is that Luke, writing for a largely Gentile audience and with particular theological aims, judged some Markan details unnecessary for his purposes.