In Jesus' day, sometimes someone around Jesus started acting bad because Satan had sent a demon to their mind to try to make them bad like him. It doesn't happen any more today.
This always happened to people who really loved God. Satan is afraid of people who love God.
One time it happened to a man who went to the synagogue every week ~ like going to church every week. He loved God and didn't want to be bad.
The demon made the man act up during worship. Jesus was there. So he made the demon leave this good man alone. The demon left for good. Jesus was stronger than the demon.
Another time Jesus went to a town with a cemetery that was made up of caves, so was very rocky.
Several of Satan's demons went into the mind of a man everyone used to like. Now he ran wild, usually among the tombs on the rocky hill.
He kept cutting himself on the rocks and hurting himself, so his former friends chained him to a rock so he wouldn't hurt himself any more. They kept him fed too.
Everyone was so sad that this once good man was now acting bad. When Jesus saw the man, the demons in him recognized Jesus.
The demons shouted through the man, "You're the Son of God!"
But Jesus did not want demons telling the world who he was. He wanted good people to tell them. So he told the demons to be quiet.
They knew Jesus was stronger than them and their master, Satan. They also knew Jesus was going to make them leave the man they were in alone.
When Jesus made the demons leave the man alone, he wanted to go with Jesus as he preached everywhere. Jesus told the man who was now good again to go back home and tell his friends that Jesus is the Son of God and loves them.
Do you know anyone who used to be good and then turned bad? Try going to that person and telling them God wants them to tell other people how much he loves them. Maybe he will stop being bad then and do the right thing.