What does Mark 4:20 mean?
The parable of the sower is a metaphor for why the people described in Mark chapter 3 reacted to Jesus in such varying ways. The seeds that land on the good soil represent the disciples (Mark 3:13–19), those whom Jesus calls His family (Mark 3:32–35), and anyone who asks for further clarification into the parable (Mark 4:10). But while the gospel and the gift of salvation are free, they aren't passive.Ephesians 2:8–9 clearly says that salvation is not dependent on any work we can do. It is impossible to be "good" enough to earn our way into heaven. Salvation is because of the work of Jesus on the cross, and He continues that work in us for a purpose (Philippians 1:6). "For we are his workmanship, created in Christ Jesus for good works, which God prepared beforehand, that we should walk in them" (Ephesians 2:10).
Jesus goes into this concept more deeply in the parable of the talents (Matthew 25:14–30). The Holy Spirit equips us, gives us gifts (Romans 12:6–8; 1 Corinthians 12:4–11, 28) and even does the heavy lifting (John 16:7–11). We are responsible for using the resources He has given us for the kingdom of God. And yet both the ability and the desire to do so are also gifts of God (Philippians 2:13).
Although Jesus did the work of the gospel by dying on the cross and rising again, we are called to do the work of spreading the gospel. In John 14:12, He promises that those who believe in Him will do greater works than He. "Greater works" not meaning more powerful, but farther-reaching. In Colossians 1:24, Paul explains that his ministry to spread the gospel fills up what was "lacking in Christ's afflictions."