What demons know and are capable of doing
The Bible teaches that demons believe in God, not in a sense that they are granted salvation because that is an impossibility according to Christian theology, but that they acknowledge God's existence. Verses used to support this idea include the following:
Matthew 8:29, “What do you want with us, Son of God?” they shouted. “Have you come here to torture us before the appointed time?” (NIV)
Mark 1:23-24, "Just then a man in their synagogue who was possessed by an impure spirit cried out, 24 “What do you want with us, Jesus of Nazareth? Have you come to destroy us? I know who you are—the Holy One of God!”." (NIV)
James 2:19, "You believe that there is one God. Good! Even the demons believe that—and shudder.." (NIV)