An old thread but an updated textual commentary:
[Matthew] 17:21 omit verse {A}
After Matt. 17:20, the majority of Greek manuscripts read τοῦτο δὲ τὸ γένος οὐκ ἐκπορεύεται εἰ μὴ ἐν προσευχῇ καὶ νηστείᾳ (‘but this kind does not come out except by prayer and fasting’; 012 04 05 019 etc.). This is lacking from ten Greek manuscripts, most of them considered to be important, and witnesses to each early translation (01* 03 038 0281 33 579 788 892* 1604 2680 [see TuT Matthew TS53]; latvl-pt syc, s cpa co, bo-pt ethms). There is no obvious reason for a mechanical omission, and the extra text is close to the parallel at Mark 9:29, where it fits the context better: an early reader may have felt that Jesus’ answer to the disciples was incomplete and therefore added the more direct response from memory (including the variant with the last two words; see Mark 9:29 below). This is one of three additional verses in the Byzantine tradition of Matthew (see also Matt. 18:11 and 23:14), which are also excluded from the editorial text of the SBLGNT and THGNT.
Houghton, H. A. G. 2025. A Textual Commentary on the Greek New Testament: A Companion to the Sixth Edition of the United Bible Societies’ Greek New Testament. Stuttgart: Deutsche Bibelgesellschaft.
[Matthew] 17:21 omit verse {A}
After Matt. 17:20, the majority of Greek manuscripts read τοῦτο δὲ τὸ γένος οὐκ ἐκπορεύεται εἰ μὴ ἐν προσευχῇ καὶ νηστείᾳ (‘but this kind does not come out except by prayer and fasting’; 012 04 05 019 etc.). This is lacking from ten Greek manuscripts, most of them considered to be important, and witnesses to each early translation (01* 03 038 0281 33 579 788 892* 1604 2680 [see TuT Matthew TS53]; latvl-pt syc, s cpa co, bo-pt ethms). There is no obvious reason for a mechanical omission, and the extra text is close to the parallel at Mark 9:29, where it fits the context better: an early reader may have felt that Jesus’ answer to the disciples was incomplete and therefore added the more direct response from memory (including the variant with the last two words; see Mark 9:29 below). This is one of three additional verses in the Byzantine tradition of Matthew (see also Matt. 18:11 and 23:14), which are also excluded from the editorial text of the SBLGNT and THGNT.
Houghton, H. A. G. 2025. A Textual Commentary on the Greek New Testament: A Companion to the Sixth Edition of the United Bible Societies’ Greek New Testament. Stuttgart: Deutsche Bibelgesellschaft.