The first thing to recognize is that, after this incident, the boy left with complete healing: The demon left forever, and the boy was restored fully. There was a failure involved—the only such failure ever recorded—and that was by the apostles. How easy it would have been for apostolic writers to bypass this incident. But they did not. They showed their own flaws, their own foolish blindness at the time, and that honesty makes their testimony all the more powerful.
If some enter with assistance, such as crutches or wheel chairs, how do they leave?
Until the incident of Mark 9, the apostles—even in their spiritual immaturity—had enjoyed many successes. Of the twelve apostles, Scripture says, “They cast out many demons and anointed with oil many who were sick and healed them” (Mark 6:13). Of the wider group of disciples, Scripture says, “The seventy-two returned with joy, saying, ‘Lord, even the demons are subject to us in Your name’” (Luke 10:17). Before the Mark 9 event, success was the pattern for Jesus’ followers.
As far as the record goes, the failure of Mark 9 was a single exception. And we know what went wrong: The disciples lacked prayer (Mark 9:29). They encountered a spirit that put up resistance, and Jesus showed that “this kind” of spirit could be driven out only by prayer. Perhaps the disciples had taken for granted that their command alone would work every time. The fact that the disciples were not praying, or not praying sufficiently, may suggest that they had grown complacent after so many successes. After the Mark 9 event, with its lesson on the need for prayer, success was the continuing pattern. Is that the continuing pattern you see today for those who claim to perform miracles? Do they attempt the full range of healings and miracles? More than attempting, do they succeed? Do all present speak highly of their obviously supernatural power? This was what was said about Jesus:
[The people] were astonished beyond measure, saying, “He has done all things well. He even makes the deaf hear and the mute speak” (Mark 7:37).