Generation of Jesus Christ
Matthew starts his gospel with the answer to his riddle. He will list forty-one generations in the genealogy of Jesus, then say there are forty-two. Where is the last one? The mystery generation are those whom he will call brother, sister and mother. Though Mark has the saying that those who do his will shall be called such, he could not include it as a riddle since he did not yet see that he literal history of Israel was itself a parable and riddle.
Matthew will use the literal history as prophecy and show how Israel acted out the parable of Christ in many ways. This is the book of his family as he lived among them and taught them.