What does Revelation 22:18 mean?

This verse offers a stern warning not to add to the words of Revelation; the next verse also condemns those who would attempt to censor it. Adding to the book of Revelation brings God's judgment: plagues will fall on the one who adds to Revelation. This might take the form of attempting to add words or prophecies in a very literal way. It might also refer to those who try to make this writing say things it does not say: warping the text for their own ends.

Adding comments, content, or interpretations which minimize Revelation's commands and promises is tantamount to calling the Holy Spirit, who inspired the book, a liar. When Moses gave God's statutes and rules to Israel, he warned, "You shall not add to the word that I command you, nor take from it, that you may keep the commandments of the LORD your God that I command you" (Deuteronomy 4:2). Also, in Deuteronomy 12:32, the Lord warned: "Everything that I command you, you shall be careful to do. You shall not add to it or take from it." Proverbs 30:5–6 says, "Every word of God proves true…Do not add to his words, lest he rebuke you and you be found a liar."

God's Word is perfect and authoritative and needs no human additions. A message as complex as Revelation, in particular, cannot be manipulated without risking severe error. Though this warning is technically in reference to Revelation itself, the general principle is a good one to apply across all of Scripture (1 Corinthians 4:6).