Revelation 1:2 2who witnessed the word of God and the witness of Jesus Christ [and] the things he saw.
John reflects on the same ideas he wrote about in John 1:1-4, 14: the Word of God became flesh, and people saw, heard, and touched him (1 John 1:1). The opening phrase is also found in 1:9 and reversed in 20:4. The word of God could also be interpreted the word from God. John was a witness to the claims he makes in this book and his other writings. This verse adds authority to what John writes because of his association with Jesus as a living eyewitness. The Book of Revelation is further testimony about the living Word.
The difference between the Gospel of John and the Book of Revelation is that the Word has now been raised from the dead, exalted, and seated at the right hand of God. The man from Nazareth who wandered around preaching and performing miracles is the same one John saw in his vision, exalted and coming again in glory. Revelation confirms the person of Jesus Christ as described in the Gospels. We accept by faith that John’s testimony is valid and true. In typical Jewish interpretation based on Deuteronomy 19:15, John gives two witnesses to confirm the truth of his claim: his own and that of Jesus Christ. The implied question is, will readers accept and believe these words? Faith will be shown by 1) enduring through suffering, and 2) holy living in the midst of an increasingly evil and corrupt world.