There is a close connection between the various parts of this passage. The Parable of the Sower (4:3–9) is followed by a discussion with the disciples about speaking in parables (4:10–12). After that, Mark gives the explanation of the parable (4:13–20), to which a recapitulation is added (4:21–25). Thus, both the parable as well as its explanation are followed by a more general section. Consequently the structure of the passage as a whole (A-B-a-b) displays a clear internal coherence.1
1 Again he began to teach beside the sea. And a very large crowd gathered about him, so that he got into a boat and sat in it on the sea, and the whole crowd was beside the sea on the land.