Mark mostly tells us what Jesus did, more than what he said, but in Chapter 4 (as well as Chapter 13) he emphasizes what Jesus taught. Here Jesus is teaching from the water, protecting him from the encroaching mob.

He commands his followers to listen!

In the parable of the sower, he describes the various kinds of people who have encountered his ministry.

Jesus says he's given his followers the ability to understand the parables, so it's easy to worry if you don't understand them right away. Those who are not his followers will give up or not care; if you care enough to pursue understanding, you have nothing to worry about. Come to him and ask him to reveal it to you!

Isaiah 6 shows us the inability to understand Jesus, caused by hardness of heart, is associated with the destruction of Jerusalem. The city will eventually fall because of the hardness of their hearts.

Jesus implies that understanding this parable is the key to understanding all of them; spreading the gospel is our kingdom work! We must hear it, accept it, and bear fruit by sharing it. This is the mission of the Kingdom!