The question, “have you come to destroy us?” shows that he believes that Jesus’ intention is judgment. His arrival in Capernaum is to the detriment of the citizens. He warns the people who are unsure about Jesus’ action: this authority (Mark 1:22) will lead to their death!
This shows the eternal ignorance of demons for God’s love. The demon knows what the Israelites, as sinners, deserve. He also knows God’s holiness. That is why he believes that Jesus’ action can lead only to death and destruction. His blind spot concerns the reason Jesus came to earth, namely, that the Holy God, through the sacrifice of his Son, is going to bring about reconciliation between himself and sinners (also in Capernaum). The love with which Jesus teaches his people matches that. The suggestion made by the unclean spirit betrays his inability to understand love. Jesus’ coming can mean death to Capernaum, but only if the inhabitants reject his doctrine and his love. Christ performed many miracles in the city and when true repentance fails to occur, the threat of judgment comes (see Luke 10:13–16). Then it looks as though the unclean spirit was right after all. But that destruction does not come about through the coming of Jesus of Nazareth, but through the power of unbelief that was evident first in this unclean spirit and that was stimulated by his opposition.1
24 “What have you to do with us, Jesus of Nazareth? Have you come to destroy us? I know who you are the Holy One of God.”