What does Matthew 13:51 mean?

This extended section of Jesus' teaching began in verse 36. Jesus and the disciples left behind the crowds and entered a house together. The disciples asked Jesus to explain the meaning behind one of the parables (Matthew 13:36). Jesus has done so both by spelling out the meaning of that parable and adding several new parables to it.

Now Jesus asks His disciples if they grasp what they've been told. The disciples claim they do—but it's certain they don't understand as well as they think they do. As the gospels continue to explain their interaction with Jesus, the disciples will demonstrate further confusion about the truths being presented. Many examples of this will be recorded in the next chapters of Matthew (Matthew 13:21–23; 26:6–13). Of course, thanks to instruction from Christ, these men had better understanding of the kingdom of heaven than before.

Jesus' teaching about the kingdom must have introduced them to several new ideas. Like most Jewish people of that era, they likely expected the Messiah to immediately overthrow Israel's enemies and set up Israel to prosper in the world. Jesus has taught, in parables, that the kingdom will start small and grow large over time (Matthew 13:31–32). He has also taught that the righteous and the wicked will live together, side by side, until the day of judgment comes (Matthew 13:24–30). Still, it is worth any sacrifice to be included in the kingdom (Matthew 13:44–46) because a day of judgment is coming in which the evil will be removed and thrown into the fiery furnace by the angels of God (Matthew 13:47–50).

Even as a partial picture of what is to come, that would have been a lot to take in. Whatever Jesus' core group of disciples truly understood, it required adjustment. They had to re-assess their expectations for what the coming kingdom would be like. In the following verse, Jesus will show why it is important for them to continue to work at understanding what He is teaching.