It discusses the work of John the Baptist. The Pharisees came to John to be baptized and he refused. Then he really lets them have it. He gives a message to them which is intended to wake them up. Baptism is not a work they do just for show.
Baptism reflects true repentance in the heart.
The Pharisees did not have this and were instead trying to use baptism to deceive others. So John went on baptizing and calling people to true confession of their sins and repentance from the sinful lifestyle. In today's reading, Jesus comes to John to be baptized. John doesn't feel that would be right, but after Jesus explains things, John consents. As Jesus comes up from the water, the Holy Spirit descends upon Him, looking like a dove, and then the Father speaks words identifying Jesus.