These verses explain the parable from Matthew 13:24–30. The people of the kingdom (like wheat) live side by side with those who do not belong to it (like weeds). The “field” is the world, and this will continue until the end of history.
The mystery of the kingdom is that it is already present in the world, but God has not yet removed the wicked in judgment. The disciples of Jesus must learn patience and trust God’s timing.