A benediction of this type is quite unusual at the conclusion of an apocalyptic writing, but it is quite fitting for this one which incorporates epistolary features for the churches and is to be read in them (Rev. 1:3-4+).2
1 Bruce M. Metzger, A Textual Commentary on the Greek New Testament (Stuttgart, Germany: Deutsche Bibelgesellschaft, 1994), Rev. 22:21.
2 Robert L. Thomas, Revelation 8-22 (Chicago, IL: Moody Press, 1995), Rev. 22:21.