I testify: John swears to protect the integrity of the Book of Revelation. He curses anyone who changes the book's content or message (compare Deuteronomy 4:2; 12:32). This curse contrasts with the blessing for those who read aloud, listen to, and follow the prophecy (Revelation 1:3). When Revelation was written, scribes sometimes changed books to fit their views. Early Christians quickly developed ways to verify messages and messengers (see John 21:24; 1 Corinthians 16:21; Galatians 6:11; Colossians 4:18; 2 Thessalonians 3:17; 1 John 4:1–3).
Since the early church, the New Testament's scope and content have defined Christian teachings. However, some still try to change Scripture by adding works they consider equal to the Bible or by claiming parts of the Bible are unreliable. The true church has rejected and will continue to reject these attempts to change the canon, viewing them as human or even demonic efforts to alter the foundation of the Christian faith.