“Now he was casting out a demon that was mute; when the demon had gone out, the one who had been mute spoke, and the crowds were amazed. But some of them said, ‘He casts out demons by Beelzebul, the ruler of the demons.’ Others, to test him, kept demanding from him a sign from heaven. But he knew what they were thinking and said to them, ‘Every kingdom divided against itself becomes a desert, and house falls on house. If Satan also is divided against himself, how will his kingdom stand? —for you say that I cast out the demons by Beelzebul, by whom do your sons cast them out? Therefore they will be your judges. But if I cast out demons with the finger of God, surely the kingdom of God has come upon you. When a strong man, fully armed, guards his own palace, his goods are in peace. But when a stronger than he comes upon him and overcomes him, he takes from him all his armor in which he trusted, and divides his spoils. He who is not with me is against me, and he who does not gather with me scatters.’” (Lk 11: 14-23)
Here the Lord seems to contradict what He said in Mk 9: 38-40. There, when the Apostle John complained about a certain someone driving out demons in the Lord’s name but was not one of the Apostles (“not one of us,” as John says), the Lord responded: “Do not stop him. For no one who does a miracle in my name can in the next moment say anything bad about me, for whoever is not against us is for us.”
Why are the Lord’s responses different in the two passages? 1. In Lk 11: 23 (“He who is not with me is against me…”), Jesus is talking not about a human being but about the devil, whose will to be “against” God has been determined once and for all in the timeless, invisible world of the angels and demons; and 2. In the two passages in question, Jesus is addressing two different audiences, with very different concerns and perspectives. In Mk 9: 40 (“…whoever is not against us is for us”), He is addressing His own disciples, who are concerned with “identity politics” of this world, as to who is “one of” them; while in Lk 11: 23 He is addressing those who did not follow Him, and who posed questions about His alliances on the invisible battleground with the “wolf” (or devil), who aims to “scatter the sheep” (Jn 10: 12). As mentioned above, it is the devil Jesus is talking about, when He says, “He who is not with me is against me, and he who does not gather with me scatters.” Don’t know if this explanation is clear, but it’s all I’ve got on the topic.