Many modern Bibles move this sentence to a footnote. The earliest Greek witnesses behind the critical text omit the entire verse, while the received text and the broad later tradition keep it. Its words resemble Mark 9:29, where Jesus says that “this kind” can come forth by prayer and, in the received form, fasting.
“Howbeit this kind goeth not out but by prayer and fasting.” — Matthew 17:21
The likeness to Mark supplies the chief case against Matthew 17:21. It does not settle the case.
A saying at home in the scene
The disciples had attempted an exorcism without success. Jesus rebukes their unbelief, speaks of mustard-seed faith, and then names the discipline required in this hard case. Prayer confesses dependence. Fasting gives bodily form to earnest self-denial. Neither is a technique that forces God’s hand.
The verse does not interrupt the answer. It completes it. Unbelief is answered not by loud confidence but by a life turned toward God.
Critics argue that a copyist imported the line from Mark to make Matthew’s explanation fuller. The whole-verse omission in Sinaiticus, Vaticanus, and allied witnesses gives that claim force. There is also no obvious single-letter accident that must account for the shorter form.
Yet parallel truth is not foreign truth. Jesus may repeat the same instruction in the same historical incident; Matthew and Mark may both report it. Scribes also shortened passages when a sentence seemed duplicated elsewhere, especially when a lection moved from the healing to the next scene without requiring the private explanation. A smooth omission can spread without leaving broken grammar.
Prayer and fasting are not magic
The verse has sometimes been abused as though longer fasting purchases greater spiritual rank. Christ gives no scale and promises no spectacle. Scripture condemns fasting performed for human praise. True fasting humbles the body before God and joins prayer when need presses hard.
Nor does the command reduce every affliction to a devil needing an elite exorcist. “This kind” belongs to the case before the disciples. The authority remains Christ’s; the servants must not act as if a former commission made present dependence needless.
Matthew 17:21 has wide church use, a natural place in the answer, and wording that is demanding rather than decorative. The Markan parallel explains why a scribe might add it, but it also confirms that the Lord gave such instruction. The received sentence should stay where the Church has long read it: between failed self-reliance and the renewed walk with Christ.
Prayer and fasting also belong together without becoming inseparable rules for every request. Scripture records prayer without fasting and fasting joined to solemn prayer at moments of need, repentance, and appointment. The pairing in this case marks unusual dependence, not a universal timetable.
The variant at Mark 9:29—where some texts retain prayer but omit fasting—likely influenced how readers approached Matthew. A copyist or editor accustomed to the shorter Mark may find Matthew’s whole verse suspect. Another may fill Matthew from the full Mark. The parallel history must be weighed in both Gospels rather than used as a single automatic answer.
The verse’s ascetic use in the church can cut two ways as evidence. Devotion may preserve a difficult command in memory; devotion may also expand a text. Its exact fit with the failed exorcism and the received breadth remain the firmer grounds for inclusion.
Sources and further reading
- Matthew 6:16–18; 17:14–22; Mark 9:14–29.
- Bruce M. Metzger, A Textual Commentary on the Greek New Testament, note on Matthew 17:21.
- John William Burgon, The Causes of the Corruption of the Traditional Text of the Holy Gospels.