Chapter four contains one of the longest sections in Mark dedicated to Jesus’ teaching, apart from Passion Week. Even then, except for the last few verses, chapter four contains just four parables and the explanation of the purpose of Jesus’ parables. The purpose, first mentioned in Isaiah 6:9-10, was so that believers would receive new truths, while unbelievers would not be able to understand them, keeping them from heaping additional judgment upon themselves for rejecting it. From this point on, Jesus spoke in parables to the crowds but explained them to the disciples (Mark 4:10-12, 33-34).
First is the parable of the sower and the seed (Mark 4:1-9, 13-20). One of the few parables that Jesus explained in detail, he illustrated how the word is spread out to people, like seed is scattered in a field. People respond differently, depending on their life circumstances. From some, Satan steals it away immediately (see 2 Corinthians 4:4). Others receive it but quickly turn away because of personal persecution or other priorities. Some do receive the word, let it grow in them, and produce a varied harvest for God.
Second is the parable of the lamp (Mark 4:21-25), which illustrates that the things we have from God are not to be hidden away but rather used. Some rewards and blessings may be directly tied to the service people perform in obedience to God.
The third and fourth parables refer to the kingdom of God. In one, the kingdom is like sown seed, growing regularly, without the farmer understanding how (Mark 4:26-29). In the other, the kingdom is like a mustard seed. Even though it starts small, it grows into a massive tree, offering refuge for all the birds around it (Mark 4:30-32).
The single non-parable in this chapter recounts one of many times Jesus demonstrated his authority over creation. When the disciples were stuck in a massive storm on the Sea of Galilee, they woke him from a nap in the back of the boat (Mark 4:35-41). Their fear for their safety caused them to doubt his care for them. When he calmed the storm, their fear changed to awe as they began to realize even more what his claims really meant.