When he arrived at the other side in the region of the Gadarenes, two demon-possessed men coming from the tombs met him. They were so violent that no one could pass that way. “What do you want with us, Son of God?” they shouted. “Have you come here to torture us before the appointed time?”

Matthew 8:28-29//

Simply knowing who Jesus is will not provide salvation. Note the demons did not declare Jesus is Lord, which is part of what must happen for us to be saved. We must also believe in our heart that God raised Jesus from the dead. The demons only saw how they could be punished, which is sometimes how the world sees God. They forego His love and gift of salvation, and they only see how they can be punished because they refuse to believe.