Two themes throughout this section:
1) Repentance and the coming of the kingdom. John the Baptist preaches repentance and baptism to begin again. Jesus rejects temptation in the desert. And then Jesus goes on to preach repentance. The proclamation of the near arrival of God's kingdom is the central message of Jesus and, along with the resurrection, the basis and object of Christian hope. We have seen Jesus in humanity and suffering; we look forward to seeing His kingdom come again in faith, glory, justice, and peace on Earth.
2) The beginning of the apostles. We see the first four disciples gathered towards the end of the Chapter 4. We see their complete abandonment of previous life in order to follow Jesus. Note that this is different from the normal teacher-student behavior. Students come to the teacher to learn. Here (and following), we see Jesus gather up certain people, the closest he comes to founding a church.