Jesus left Capernaum again (after he entered it in Mark 2:1) and after that he travelled beside the sea,
that is the area around the shore of the lake of Galilee (as in Mark 1:16). The whole crowd came to him and he taught them: the tenses of the Greek verbs indicate that this concerns the depiction of the situation.
In Mark 1:45 it was already said that people were coming to Jesus from every quarter. In that way a permanent crowd of people formed who sought him continually. He had withdrawn himself from them by entering Capernaum privily (Mark 2:1), but now they were flocking toward him again and in his patience and love Jesus continues to teach them, even though the result of faith is still slight. His method of operation in this period is distinguished from the preceding period, when Jesus travelled around to the synagogues (Mark 1:39). Now he demonstrates that people cannot continue to listen to him unless they follow him to where he goes!
Especially in this period he shows that following is not a coincidental circumstance, but is characteristic of faith.1
13 He went out again beside the sea, and all the crowd was coming to him, and he was teaching them.