What does Matthew 13:48 mean?

In one of the final parables included in this chapter, Jesus once again compares the kingdom of heaven to something His listeners in and around Capernaum would have known well. In this case, the symbolism comes from fishing on the Sea of Galilee. Specifically, Jesus describes fishing with a net. This style of fishing takes many forms. Sometimes a net is stretched between two boats, or between a boat and the shore, and then dragged along the bottom of the lake. In other cases, a circular net is thrown flat onto the water and pulled down by weights. Either method results in a variety of animals being captured; not everything caught in the net is something the fishermen want or need.

What happens next is common sense, but in the context of the parable it carries an important lesson (Matthew 13:49). The contents of the net are sorted. Some are considered good, meaning they're worth eating or selling. Others are bad, meaning unusable for anything at all. The fishermen do the work of sorting through all the different kinds of fish and throwing the bad ones away while saving out the good in special containers.

Every Israelite had likely observed this process. This would have amplified the impression the parable made on those who understood the idea behind it.