I have spoken on previous occasions about Matthew's redaction of Mark as something that shows a rich understanding of what is happening in Mark, and which sometimes attempts to take Mark's interesting ideas a little further (e.g. my articles on Simon Peter and John the Baptist [PDFs]). It occurred to me recently that a lot of what is happening in Matthew might be seen as a kind of "orthodox redaction" of Mark, an attempt to fix some of the potentially troubling ideas and implications in Mark.
Take, for example, the question of Jesus' father. In Mark's Gospel, Jesus does not have a human father. He is "the craftsman, the son of Mary" (Mark 6.3); his father is in heaven and addresses Jesus directly as his son (Mark 1.11, 9.7) and Jesus calls him "Abba" (Mark 14.36). Other supernatural beings know that he is God's son too (3.11). The unwary reader of Mark might easily assume that Mark's Jesus, who simply appears on the scene as an adult in Mark 1, is some kind of god, perhaps the product of a union between a god and Mary. Matthew sees the problem. He gives Jesus a father, named Joseph; indeed, he begins the book with him (Matt. 1). In redacting the Rejection and Nazareth story, he makes Jesus "the son of the craftsman" (Matt. 13.55) so that there can be no doubt about the matter.
The same phenomenon appears elsewhere. Mark's Jesus, at his first appearance in the Gospel, goes to a baptism (Mark 1.9-10) which we have just heard characterized as a "baptism of repentance for the forgiveness of sins" (Mark 1.4). The unwary reader might easily assume that Jesus is going to John to repent and have his sins forgiven, so Matthew makes sure that there is no doubt about the matter and engages in an "orthodox redaction", making clear that this is an unexpected and anomalous event (Matt. 3.13-17).
Other examples include the abrupt ending of Mark, which concludes the story before Jesus has appeared to the disciples (Mark 16.1-8). Indeed, the last time they were seen, they were fleeing from the scene (14.50). For all the unwary reader knows, they might never have come back But Matthew knows traditions like 1 Corinthians 15, and that Jesus appeared to Peter and the twelve and that these traditions were regarded as foundational by the earliest communities (1 Cor. 15.1-3), and he provides what Mark only leaves implicit, and narrates appearances to the disciples (Matt. 28.16-20).
Matthew's orthodox redaction of Mark was so successful that we now find ourselves reading Mark through Matthew's -- and also Luke's -- eyes. His skill as a redactor with "orthodox" beliefs was that he rescued Mark from the potential to have been read and interpreted quite differently.