Expositor's Bible Commentary Commentary Mark 9:18

"and wheresoever it taketh him, it dasheth him down: and he foameth, and grindeth his teeth, and pineth away: and I spake to thy disciples that they should cast it out; and they were not able." — Mark 9:18 (ASV)

Jesus’ inquiry as to what the other disciples and the crowd were arguing about brought a reply from a man who had brought his demon-possessed and epileptic son for healing. Doubtless the disciples had fully expected to be able to exorcise the demon. Had that not been a part of their commission (cf. 3:15), and had they not already been successful at it (cf. 6:13)?