Is the warning in Revelation 22:18-19 about the entire Bible or just the book of Revelation?

TL;DR:

While the warning in Revelation 22:18-19 applies to the book itself, it echoes earlier warnings in Scripture about not changing God's Word. Since all Scripture is God-breathed and inspired, altering any part of it carries severe consequences.

what does the bible say?

While Revelation 22:18–19 applies to all of the book of Revelation specifically, it is not the only passage that warns us against changing what God has said. Indeed, that warning has been repeated from the earliest Scripture. In addition to changing the written word, He also strongly warns against those who add to His spoken word by falsely prophesying and teaching in His name. Because all of Scripture is breathed out and inspired by God, it is natural to assume that the punishment mentioned in Revelation applies to everything He said. Also, because Revelation 22:18–19 is at the end of the last book written of the Bible, it is reasonable to expect that that specific warning covers all previous books in the biblical Canon, and not just Revelation.

from the old testament

In Deuteronomy 4:2, God said, “You shall not add to the word that I command you, nor take from it.” He was referring to the commands He had given them, and the Israelites were warned not to modify them.
God repeats His warning in Deuteronomy 12:32 saying, “Everything that I command you, you shall be careful to do. You shall not add to it or take from it.” God says whatever I command you—not just “don’t change these limited sets of commands.” The principle, then, is that everything God commands comes with the same warning.
Later in Deuteronomy, God talks about those who prophesy, claiming that they are speaking God’s words. To those who add to, or contradict, His words, God says, “that prophet or that dreamer of dreams shall be put to death, because he has taught rebellion against the LORD your God … to make you leave the way in which the LORD your God commanded you to walk. So you shall purge the evil from your midst” (Deuteronomy 13:5). The penalty for claiming to be speaking on God’s behalf without actually doing so was severe—death. Why? Because those who add or take away from what God says are seducing people to not obey God.
To show it is not just limited to the Law, the book of Proverbs repeats this warning, saying, “Do not add to His words lest he rebuke you and you be found a liar” (Proverbs 30:6). Notice, first, that it is not just God’s “commands” but “His words.” This is because everything He says is truth and directly or indirectly a command. Second, the penalty is that we will be “reproved” (punished) for making any changes. Third, if we change anything that God says, we are found to be liars.

from the new testament

Revelation 22:18–19 says, “I warn everyone who hears the words of the prophecy of this book: if anyone adds to them, God will add to him the plagues described in this book, and if anyone takes away from the words of the book of this prophecy, God will take away his share in the tree of life and in the holy city, which are described in this book.”
The warning of not adding or removing from God’s Word applies to at least the entire book of Revelation as it says, “everyone who hears the words of the prophecy of this book.” Being at the end of the book strengthens the argument that everything before it in the book (all of Revelation) is covered by the warning. This means that, at the least, changing Revelation invites God’s severe judgments. Because this warning echoes God’s previous warnings in the Old Testament, the implication is that all of God’s words are covered by the prohibition.
In 2 Timothy 3:16 we read that “All Scripture is breathed out by God” (c.f., 2 Peter 1:21). The Greek word for God-breathed illustrates how Scripture is God’s word. The image is that of God speaking so closely to the page that the words are the moisture of His breath. Because all Scripture is breathed out by God, then to change any of it is to change God’s words.
Not only is all of Scripture breathed out by God, but it is alive and active. Hebrews says, “the word of God is living and active and sharper than any two-edged sword, piercing to the division of soul and spirit, of joints and marrow, and discerning the thoughts and intentions of the heart” (Hebrews 4:12). To change Scripture is to try to stop God’s words from being effective.
Paul notes that there are people who “will not endure sound teaching, but having itching ears they will accumulate for themselves teachers to suit their own passions, and will turn away from listening to the truth and wander off into myths” (2 Timothy 4:3–4). The implication of this is similar to the Deuteronomy 13:5 passage. There are teachers who change God’s Word to make it say things that appeal to people’s sinful desires, leading them to disobey God.

implications for today

Tampering with God’s word is serious business. Removing something is to remove some of God’s commands. Adding to it is to treat what God did not say as if He said it. God does not look kindly upon those who do either of those, promising to inflict severe punishment when someone does.

There are some blatant examples of religious groups changing God’s word. The Mormon church, for example, adds their “Book of Mormon” to the Bible. Jehovah Witnesses, on the other hand, have retranslated the Bible (the New World Translation) to reduce Jesus to be a lesser god and a created being.

Other groups also intentionally, though more subtly, modify God’s Word by teaching only some passages. Prosperity teachers, for example, teach just the passages that appear to say that God wants believers to be healthy and wealthy in this life, while ignoring other verses that say that suffering is the norm for believers (Romans 5:3–4) and that loving money or wealth is the root of all sorts of evil (1 Timothy 6:10).

Finally, we can also change God’s Word if we, ourselves, are not careful! Sometimes we say things like, “I believe God is telling me to do such and such.” God’s Spirit certainly does guide us, and it is right to think of God opening doors based on how our circumstances are unfolding (1 Corinthians 16:8–9). However, He has given us everything we need to navigate this life (2 Timothy 3:16–17), so we need to be very careful that we aren’t putting words into His mouth and overriding or changing what the Bible says based on our feelings or impressions!

understand

Revelation 22:18–19 specifically warns against altering the book of Revelation, but the principle of not adding to or taking away from God’s Word appears throughout Scripture.
All Scripture is God-breathed and authoritative, so changing any part of it is equivalent to altering God's own words and brings serious consequences.
The warning’s placement at the Bible’s end suggests a final caution that protects the integrity of all Scripture.

reflect

How seriously do you take the authority of every word in Scripture, and how do you seek to uphold it?
Have you ever added your own assumptions or opinions to what you believe God is saying? How can you be more careful in aligning your words and actions with His Word?
Why is it important to guide your thoughts and feelings to be based on the truth of Scripture, and how do you do it?

engage

How have we seen churches or Christian communities today unintentionally add to or subtract from God’s Word?
How should we respond when someone teaches something that contradicts or goes beyond what Scripture says?
What safeguards can we put in place—individually and as believers—to make sure we are faithfully preserving and obeying God’s Word?