While Jesus was on earth he encountered a lot of people who were demon possessed. In every case he commanded the demon to leave the person and it obeyed. Today many people don’t believe in the existence of demons and claim that those “demon possessed” people were actually mentally ill. If they are right, then the Bible reveals a new method for treating mental illness.
Then they sailed to the country of the Gerasenes, which is opposite Galilee. When Jesus had stepped out on land, there met him a man from the city who had demons. For a long time he had worn no clothes, and he had not lived in a house but among the tombs.
When he saw Jesus, he cried out and fell down before him and said with a loud voice, “What have you to do with me, Jesus, Son of the Most High God? I beg you, do not torment me.” For he had commanded the unclean spirit to come out of the man. (For many a time it had seized him. He was kept under guard and bound with chains and shackles, but he would break the bonds and be driven by the demon into the desert.)
Jesus then asked him, “What is your name?” And he said, “Legion,” for many demons had entered him. And they begged him not to command them to depart into the abyss.
Now a large herd of pigs was feeding there on the hillside, and they begged him to let them enter these. So he gave them permission.Then the demons came out of the man and entered the pigs, and the herd rushed down the steep bank into the lake and drowned. (Luke 8:26-33)