Jesus stepped into the middle of a public argument. The scribes had been questioning His disciples in front of a crowd (Mark 9:14). Barnes describes them as "debating with the disciples, and attempting to confound them." Gill says they were insulting the disciples "on account of their inability to dispossess a dumb spirit."

Matthew Henry notes that Jesus put the question to the scribes, "who, he knew, were always vexatious to his disciples, and teazing them upon every occasion." Barnes gives the sense of the question: "What is the subject of your inquiry or debate with the disciples?" By asking, Jesus took the dispute on Himself and brought what lay behind it into the open.

The scribes gave no recorded reply. Instead, "one of the multitude answered": a father who had brought his son, who had "a dumb spirit," and had asked the disciples to cast it out, "and they could not" (Mark 9:17-18). Matthew Henry observes, "The scribes made no answer, for they were confounded at his presence; the disciples made none, for they were comforted, and now left all to him." The father's answer turned everyone's attention from the argument to the suffering boy.

The verb "question" here is suzeteo, which Thayer defines as "to seek or examine together" and "to discuss, dispute." Mark uses the same verb for the scribes "questioning with" the disciples (Mark 9:14), and for the three disciples "questioning one with another" on the way down the mountain (Mark 9:10). Much of the scene was taken up with arguing or puzzling until Jesus asked His question.

The Greek texts differ on whom Jesus asked. The Textus Receptus, which the KJV follows, reads "the scribes"; other Greek editions read "them," which is why the ESV says "he asked them." Gill notes that the ancient versions differ here.

Jesus did not leave His struggling disciples alone in front of their critics. He came down from the mountain and stepped between them and the scribes with a question. Matthew Henry notes that once He came, the disciples stopped answering for themselves and left the whole matter to Him.

His question also shows what He cares about. The argument was loud, but the real matter was a father and a son in need. Once Jesus asked, that need came forward (Mark 9:17-18). This does not mean the disciples' failure was ignored. Jesus would speak to the unbelief around Him (Mark 9:19) and teach the disciples privately why they had failed (Mark 9:28-29). But first He turned the scene toward the one who needed help.