Of course I forgot to mention the recently deceased Michael Goulder. For example, the following is part of:
Briefly, [Michael Goulder] proposed that the gospels of Mark, Matthew and Luke were never intended to be accounts of what Jesus did and said during his life.
First, they were constructed as collections of illustrative stories, intended to convey the meaning of Jesus in terms of God's action in the world. In other words, they were theological statements closely connected to a catechetical function. As such, they would have been loosely rather than directly associated with the theology of Paul of Tarsus. Whereas Paul was a Jew working primarily in a non-Jewish context, the Gospels of Mark and Matthew were most probably linked with Jewish Christians. Luke's Gospel may have been the work of a convert to Judaism. (But note the word "may", which indicates a guess here, as in most scholarly works.)
Second, says Goulder, the Gospels were assembled by their authors primarily for use in worship as liturgical readings. This use would, I think, most likely have been intended also as a teaching aid. Just as the Muslim youth of today still learn the Koran by heart, so did Jewish young people in the time of Jesus and the first Jewish-Christian communities learn the Jewish scriptures. They would, I think, almost certainly have quickly tried to assemble a Christian counterpart to the Jewish scriptures as they gradually broke away from official Jewry.