What does Luke 11:15 mean?

Jesus has just healed a demon-possessed man who was mute and blind (Luke 11:14; Matthew 12:22). Isaiah 35:5–6 specifically mentions such healings as coming from the Messiah. No other prophet was recorded healing a blind or mute person. In a stunning display of spiritual blindness, the legal experts who have come from Jerusalem to observe Jesus determine He must have driven out the demon by the power of Satan.

The word Beel is the same as "Baal," which means "lord." Beel-zebul was originally a Philistine god, the lord of the flies. Beelzebul is frequently confused with "Beel-zebub," which means "lord of filth." It's uncertain if these are two distinct gods or if Beelzebul is a later derivation. By claiming that Jesus uses Beelzebul to exorcise demons, the scribes from Jerusalem are at least accusing Jesus of witchcraft, if not Satan-worship.

Jesus points out the absurdity of Satan telling his own demons to leave a man when removing the demon would cause damage to his own domain (Luke 11:17–18). Some readers wonder if this is necessarily true. Could Satan "reassign" his demons to fool people into thinking he is benevolent? That would be contrary to his behavior of "seeking someone to devour" (1 Peter 5:8). He does not need to give up ground to further his conquest.