How do they know that a demon didn't take over the boys body?

In real Christianity demons can't take over people.

The idea is that Jesus is the "good shepherd" and always around watching us and protecting us. Jesus would not let a demon harm someone. Jesus wouldn't let demons leave hell.

Jesus said that we aren't allowed to even think negative thoughts about each other, so he wouldn't be in heaven thinking that someone who's alive needs to be tortured.

He seemed nicer when he came back, he was more of a 'demon' before he fell under the ice. I did not like the character - in the extras the director says they tried not to make him unlikable - I think they failed.

This idea could have turned this mundane Christian drama into an interesting horror movie.