Revelation 22:20

We have now come to the conclusion of the whole, and that in three things: - I. Christ's farewell to his church. He seems now, after he has been discovering these things to his people on earth, to take leave of them, and return to heaven; but he parts with them in great kindness, and assures them it shall not be long before he comes again to them: Behold, I come quickly. As when he ascended into heaven, after his resurrection, he parted with a promise of his gracious presence, so here he parts with a promise of a speedy return. If any say, "Where is the promise of his coming, when so many ages have passed since this was written?" let them know he is not slack to his people, but long-suffering to his enemies: his coming will be sooner than they are aware, sooner than they are prepared, sooner than they desire; and to his people it will be seasonable. The vision is for an appointed time, and will not tarry. He will come quickly; let this word be always sounding in our ear, and let us give all diligence that we may be found of him in peace, without spot and blameless. II. The church's hearty echo to Christ's promise, 1. Declaring her firm belief of it: Amen, so it is, so it shall be. 2.

— Matthew Henry's Concise Commentary (public domain)

Amen. Even so, come--The Song of Solomon (Sol 8:14) closes with the same yearning prayer for Christ's coming. A, B, and Aleph omit "Even so," Greek, "nai": then translate for Amen, "So be it, come, Lord Jesus"; joining the "Amen," or "So be it," not with Christ's saying (for He calls Himself the "Amen" at the beginning of sentences, rather than puts it as a confirmation at the end), but with John's reply. Christ's "I come," and John's "Come," are almost coincident in time; so truly does the believer reflect the mind of his Lord.

— Jamieson-Fausset-Brown Commentary (public domain)