Then people went out to see what had happened, and they came to Jesus, and found the man from whom the demons had gone, sitting at the feet of Jesus, clothed and in his right mind; and they were afraid. And those who had seen it told them how he who had been possessed with demons was healed. Then all the people of the surrounding country of the Gerasenes asked him to depart from them; for they were seized with great fear; so he got into the boat and returned. The man from whom the demons had gone begged that he might be with him; but he sent him away, saying, "Return to your home, and declare how much God has done for you." And he went away, proclaiming throughout the whole city how much Jesus had done for him. Luke 8:35–39 (RSV)
Jesus healed the man who had been possessed by demons. He had been a terror to everyone in the area. The violence he inflicted on others had become legendary, to the point that he was left alone among the tombs.
When Jesus had arrived onshore, not far from where the man was hiding, the demons cried out in fear, fear of what Jesus might do to them. Jesus banished them, and the man was restored to himself.
A miracle of God can unsettle those who have experienced it. The man's return to sanity, the demons' flight, and their lack of understanding leads them to beg Jesus to leave. They were not ready for what God had done among them.
Understandably, the man wanted to go with Jesus. He felt alienated from the people who had driven him out into the tombs. They could not rejoice in his healing, fearfully asking Jesus to leave.
Jesus sent him home, to proclaim what God had done for him. One would think that this would be too hard to do. He goes, nonetheless, for God had given him his life. The same power that had driven the demons away now led him to share the Good News, confident in the Lord's strength at work in him.