He who testifies to these things: the same verb “to testify,” used in verses 16 and 18, here has the sense of “announce,” “proclaim.” The speaker is Jesus, and these things are the visions and revelations that he has proclaimed and that are recorded in this book. The meaning may be expressed by “He who declares these messages.”
Surely I am coming soon: as in verses 7 and 12.
Amen. Come, Lord Jesus!: the initial Amen may be translated “So be it” or “May it be so” (see 1.6). The speaker is John, the writer of the book. Come, Lord Jesus is the Greek equivalent of the Aramaic Marana tha (1 Cor 16.22, “Our Lord, come!”).
Quoted with permission from Bratcher, Robert G. and Hatton, Howard A. A Handbook on The Revelation to John. (UBS Handbook Series). New York: UBS, 1993. For this and other handbooks for translators see here .