There is an interesting textual issue surrounding Mark 9:29 and Matthew 17:21. When Jesus came down from the mount of transfiguration he found that some of his disciples had unsuccessfully attempted to exorcise a demonic presence from a young boy. After Jesus cast the demon out and healed the boy, Matthew and Mark record that his disciples asked him why they had not been able to drive the demon away.
In the King James Version, Jesus provides this answer:
This kind goeth not out but by prayer and fasting. (Matthew 17:21)
This kind can come forth by nothing, but by prayer and fasting. (Mark 9:29)
More recent translations omit “and fasting” from Mark 9:29 and eliminate Matthew 17:21 completely. In Mark, then, “this kind” come out by prayer alone and in Matthew the disciple’s failure is solely a sign of too little faith.
Briefly, the difference between translations is the result of differences that exist in the ancient, hand-copied manuscripts of the Biblical text. The majority of manuscripts include the “prayer and fasting” language in both Matthew and Mark. Some of the very oldest manuscripts, however, do not. And, significantly, the same manuscripts that include those words in Mark also include them in Matthew. Because changes tend to be duplicated from one generation of hand-copied manuscripts to the next, scholars give the most weight to the oldest manuscripts. That is, however, not an infallible rule. The oldest known manuscripts may reflect changes that occurred prior to their being produced. We may just be missing still older and and intermediate manuscripts which contain the same text as later versions. The manuscripts we have available to us represent only a fragment of the manuscripts produced. And since thousands of manuscripts circulated in various forms across the vast ancient world, we can’t be certain who copied from whom. So scholars also apply other criteria when they evaluate variations among ancient manuscripts.
I think that modern translators are probably correct. “Prayer and fasting” was probably added to the text by a later scribe. Perhaps it all started with a note in the margin later copied into the main body of the text by others. But that raises the question of why. Why would some early Christians associate prayer and fasting with exorcism?
First, we see that association in the life of Jesus himself. Jesus’ most significant encounter with Satan took place in the context of prayer and fasting. Jesus fasted 40 days and was tempted by the Devil. In Matthew, the temptation ends with an exorcism: Be gone, Satan!
Second, the early church believed in the power of exorcism and practiced ritual exorcism as part of its pre-baptismal preparation, a practice preceded and accompanied by a period of prayer and fasting. This period of preparation evolved into Lent, readying candidates for baptism during the the great Paschal feast.
I’ll have more thoughts on both of these connections, later. As they stand, however, Matthew 17:21 and Mark 9:29 are evidence that the early church associated prayer and fasting with exorcism. Whether the “prayer and fasting” words come from the lips of Jesus, a pre-Markan saying, the hand of the evangelist or the pen of a later scribe, they demonstrate that our forebears saw a close relationship between spiritual freedom and the persistent use of the means of grace. Casting out Satan is God’s work, accomplished with God’s power. But it is also the church’s work, accomplished with prayer and fasting to call upon the cleansing and healing power of God.