We are now entering the public life of Jesus. The gospels shift to the teaching and preaching of the Lord.
Here Matthew presents the basic kernel of the mission of Jesus: "Repent, for the kingdom of heaven is at hand."
Matthew says that to show his power Jesus goes round teaching and preaching as well as healing. The Epiphany, the public showing of Jesus, has now taken place and this preaching and teaching are the first fruits of that showing.
To prove that the time has come for the new prophet to appear, Matthew uses a quote from the old testament; "Those who have lived in darkness have seen a great light." Jesus is the great light that is to come into the world.
The teaching of the Lord now begins. The church year moves on to Phase II!