What does Matthew 8:28 mean?

Jesus and His disciples have traveled by boat from one side of the Sea of Galilee, probably near Capernaum, to the other side. Specifically, they have arrived in the country of the Gadarenes. Gadara and Gerasa (Mark 5:1) were Gentile cities in the region of the Decapolis, southeast of the Sea of Galilee. Jesus sailed with His disciples across the lake to get away from the crowds (Matthew 8:18).

Leaving the boat, Jesus has come ashore to an area marked by ancient tombs, perhaps in a hillside. Two demon-possessed men come out of the tombs and approach Him. Matthew describes them as so fierce nobody could pass by. Mark (Mark 5:1–20) and Luke (Luke 8:26–39), in their telling of this story, mention only one of the men and describe him as having demon-enabled supernatural strength so that he could not be bound without breaking free. He was said to be naked and living among the tombs away from all other people. Graveyards were understood to be unclean places by the Israelites.

Demon possession was understood to be a fact of life in and around Israel and in much of the ancient world. Nobody questioned the existence of demons. They had seen too many people afflicted, often violently, when occupied by demons. Demons were known to alter personalities and behaviors, as well as causing those oppressed to behave in self-destructive and violent ways. The lesser occurrences of demon possession today is likely a deliberate strategy by the Devil: disbelief in the spiritual world is a more potent weapon today than it would have been in Jesus' era.