en_tn_condensed/rev/22/18.md

General Information:

John gives his final remarks.

I testify

Here "I" refers to John.

the words of the prophecy of this book

Here "words" refers to a message. See how you translated this in Revelation 22:7. Alternate translation: "the prophetic message of this book" (See: rc://en/ta/man/translate/figs-metonymy)

If anyone adds to them ... God will add

This is a strong warning to not change anything about this prophecy.

that are written about in this book

This can be stated in active form. Alternate translation: "which I have written about in this book" (See: rc://en/ta/man/translate/figs-activepassive)