Albert Barnes' Notes on the Whole Bible - Mark 9:39
Forbid him not - Do not prevent his doing good. If he can work a miracle in my name, it is sufficient proof of attachment to me, and he should not be prevented.Can lightly speak evil of me - The word here rendered “lightly” means quickly or “immediately.” The meaning of the passage is, that he to whom God gave the power of working a miracle, by that gave evidence that he could not be found among the enemies of Jesus. He ought not, therefore, to be prevented from doing it. There is no reason to... read more
The Pulpit Commentary - Mark 9:39
But Jesus said, Forbid him not. It is as though our Lord said, "Do not forbid him; do not hinder him from a good work—a work which does honor to me and to my cause; because, although he does not actually follow me as you do, he is nevertheless engaged in the same cause; he is celebrating my Name by the casting out of evil spirits. Therefore he is not opposing my Name; on the contrary, he is publishing and recommending it." Here is a warning against that exclusive spirit, which is eager for... read more