Charles Ellicott Commentary Matthew 17:16

"And I brought him to thy disciples, and they could not cure him." — Matthew 17:16 (ASV)

They could not cure him—This, then, would seem to have been the subject of the debate. The scribes were taunting the disciples, who had probably trusted their use of the customary formula of their Master’s name and were now wrangling in their own defense. Neither the scribes nor the disciples had thought of gaining the spiritual power that could prevail through the means they both recognized as effective.