Mark 5:15 And they came to Jesus and saw the demon-possessed man, the one who had had the legion, sitting there, clothed and in his right mind, and they were afraid. 16 And those who had seen it described to them what had happened to the demon-possessed man and to the pigs. 17 And they began to beg Jesus to depart from their region. 18 As he was getting into the boat, the man who had been possessed with demons begged him that he might be with him. 19 And he did not permit him but said to him, “Go home to your friends and tell them how much the Lord has done for you, and how he has had mercy on you.”
This community sees one of the most amazing examples of life-change in history, and instead of feeling joy for this man, they are afraid of Jesus. When Jesus comes into lives, he will bring tremendous change. This passage is a reminder that people don't always respond positively to that change.
But we should follow the Lord's command - Go and tell them how much the Lord has done for us.