What does Mark 4:3 mean?

The word translated "listen" is from the Greek root word akouo. It means "to pay close attention and strive to understand what is being said." Listening and teaching are the themes for the entire chapter. Through several different parables, Jesus talks about how to listen, what we should listen to, how we should pass on what we've heard, and what we should expect in response. The direct instructions are repeated at the end of this parable (Mark 4:9), and after Jesus explains what the people should do with what they've heard (Mark 4:24).

In the Old Testament, the idea of "sowing" is related to the blessings God will give Israel in the future. He will "sow" in Israel, and their population and blessings will be renewed (Jeremiah 31:27–28; Ezekiel 36:9–11; Hosea 2:21–23). In this parable, the sower is anyone who teaches the gospel. At first, the sower is Jesus, but He is training the twelve to join Him in that work (Mark 3:13–14; 6:7–13), and He does the same for believers today.

Just as a farmer can't sow seeds he doesn't have, we can't teach what we don't understand. We need to understand God's Word well in order to teach others. In the parable of the sower, Jesus uses the metaphor of good soil accepting the seed of the gospel to represent those who willingly accept His words. We need to be the good soil before we can be the sower.