Albert Barnes Commentary Mark 9:39

"But Jesus said, Forbid him not: for there is no man who shall do a mighty work in my name, and be able quickly to speak evil of me." — Mark 9:39 (ASV)

Forbid him not. Do not prevent him from doing good. If he can work a miracle in my name, it is sufficient proof of his 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 the one to whom God gave the power of working a miracle thereby gave evidence that he could not soon be found among the enemies of Jesus. Therefore, he ought not to be prevented from doing it.

There is no reason to think, here, that John had any improper designs in opposing the man. He thought it was evidence that he could not be right because he did not join them and follow the Savior. Our Lord thought differently. He opposed no one who gave evidence that he loved him.

Wherever he might be, or whatever his work, yet, if he did it in the name of Jesus and with the approval of God, it was sufficient evidence that he was right. Christians should rejoice in good done by their brothers of any denomination. There are men calling themselves Christians who seem to look with doubt and suspicion on all that is done by those who do not walk with them.

They undervalue their labors, attempt to lessen the evidence of their success, and to diminish their influence. True likeness to the Savior would lead us to rejoice in all the good accomplished, by whomever it may be done, and to rejoice that the kingdom of Christ is advanced, whether by a Presbyterian, an Episcopalian, a Baptist, or a Methodist. .