This is a difficult case to make, because Revelation has come under scrutiny for its authenticity and message repeatedly, beginning almost immediately after it was written. Revelation is distinguished by its otherworldly tone and fantastical depictions of monsters and spiritual armies; this seems wholly unfitting with many of the more personal, optimistic and "rational" arguments and characters in the New Testament. Nevertheless, Revelation fulfills several important roles both in its inclusion in the Bible, as well as in its placement as the final book in most bindings.
- Revelation gives Christ numerous opportunities to be challenged by, and be victorious over, the forces of evil. It shows that Christ will endure any and all powers that evil can muster, even if Man cannot.
- Revelation establishes, with a sense of finality, that there is a definite end of the world, to which all should be minded. Just as our own lives end, so will mortal existence itself.
- Revelation shows that God has it within his power to eliminate Satan's influence forever, and that this will be done. This gives rise to questions such as "why does God allow Satan's power to persist?" which lends strength to the argument that sin is a choice God allows us to make.
- If one chooses to interpret Revelation in a largely symbolic manner, it serves as a powerful historical account of the struggles early Christians faced, particularly with how to fit into a society that was so antithetical to their beliefs. Revelation serves to show that, regardless of its earthly power, no manmade kingdom can compare to the power of God's kingdom.
- Revelation reaffirms that Christ's life and importance was not confined to his own lifetime, and his power immense and eternal; he speaks to John, and to the reader, thus;
Fear not; I am the first and the last: I am he that liveth, and was dead; and, behold, I am alive for evermore, Amen; and have the keys of hell and of death.
All of these elements make Revelation an important "bookend" that completes the story of Christian faith by giving a sort of climax, tying up loose ends, and depicting the future not as a murky series of vague promises, but as a vivid, specific prophecy.
The book of Revelation shows us the prophecy of what we are living in these days. In this book it say that the end of times will come when a lot of natural disasters begin to happen. This book was written a long time ago yet we are living what it says. John wrote this while being exiled in the island of Pathos being boiled alive. This where the Christian faith has their trust in that Jesus will be returning for his church soon
The New Testament is evidence of what is said in the Old testament. All prophecies were completed in the New Testament. In the old testament, they predicted a Messiah, and Jesus comes in the New Testament. The reason why Revelation is in the New Testament because it is what is to come; the end of the world. It's the future and it is yet to happen.
I would like to preface this answer by stating that it is purely my opinion.
Just as Isaiah is a prophetic account of the coming of Christ (which could be argued to be the beggining of time as we know it, considering how we date eras B.C. and A.D.) Revelation is a prophecy telling of the second coming of Christ and subsequently the end of the world. It was important to the living disciples then, and is important to Christains now, that Christ fufills his promise and returns for his believers. Relevation is that promise.
Paul wrote in a time of great distress for Christians. They needed hope that their persecution would be rewarded in the end. If nothing else it should be included as a historical depiction of the desperation Christians felt as a result of their oppression by the Romans.
In a more modern sense, Christians still need hope: hope that good will conquer evil, that Christ will come back for his followers, and that God's love will conquer all. Revelation is the fairytale ending to the Bible in which satan is demolished and we all ride off into the sunset, even if the imagery is a bit demented.