The verb to hear
appears to be the crucial word in the interpretation of the parables.1 It brackets the first parable of the sower (Mark 4:3, Mark 4:9), appears twice in the quotation from Isaiah 6:9 (Mark 4:12), and each soil hears but reacts differently (Mark 4:15–16, Mark 4:18, Mark 4:20). The command to hear also concludes the parable of the Lamp (Mark 4:23) and precedes the parable of the seed growing (Mark 4:24). Finally it is also found in the conclusion of the discourse (Mark 4:33).
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.