The book opens with the good news of Jesus Christ, the Son of God, and with Isaiah's prophecy of a messenger who prepares the way of the Lord. That messenger is John the Baptist, who preaches in the wilderness a baptism of repentance for the forgiveness of sins. He wears camel hair, eats locusts and wild honey, and announces that someone mightier is coming who will baptize with the Holy Spirit.
Jesus comes from Nazareth in Galilee and is baptized by John in the Jordan. As he comes up out of the water he sees the heavens torn open and the Spirit descending like a dove, and a voice from heaven calls him the beloved Son. The Spirit drives him into the wilderness, where for forty days he is tempted by Satan, lives among wild animals and is served by angels. After John is arrested, Jesus proclaims in Galilee that the time is fulfilled and the kingdom of God is near, and he calls people to believe the gospel.
Beside the Sea of Galilee he calls Simon and Andrew, and then James and John, who leave their nets to follow him. In the synagogue at Capernaum he teaches with an authority that amazes the people and casts out an unclean spirit. He heals Simon's mother-in-law and, that evening, many who are sick or oppressed by demons. Early the next morning he prays in a solitary place, tours the villages of Galilee and cleanses a leper, whom he tells to show himself to the priest and say nothing; the man spreads the news anyway, and Jesus can no longer enter towns openly.