The final book of the Bible, Revelation, has held a grip on me since I joined a small group of high school and college students studying it in the summer of 1990. Shortly after that study and reading the book This Present Darkness (Peretti) and spending time in prayer for a young woman who was my peer (I was 20 at the time), I returned for my junior of college. And I heard God call me into vocational ministry. Revelation is exceedingly interesting to me and is also closely tied to the days I heard God tell me distinctly that I would be a pastor.
Since 1990, I have learned much about Revelation. There are many ways of reading this book of the Bible. There is the fantasizing speculation (books like The Left Behind Series), there is complete misreading (Hal Lindsey's Late, Great Planet Earth), devotional reading, and historical-critical reading. The best commentary on Revelation I have found is by Craig Keener in the NIV Application Series. The most thorough work I have read is David Aune's commentary in the Word Biblical Commentary Series.
Aune's work is not very accessible for non-scholars. I have trouble with it because my Greek is very elementary. I have a limited understanding of Hellenistic Greek vocabulary, and my knowledge of the grammar is even weaker. Aune writes in a scholarly style that requires a lot of effort for me to read. That said, I appreciate the great detail he goes to in pursuing lines of argument. His books is over 300 pages (not counting a 200-page introduction) and he only covers Revelation 1-5.
One of the topics he deals with is genre. When a Christian reads Revelation, what exactly is she reading? If someone reads Romans, the genre is obvious. It's an epistle, a letter. Isaiah is a prophecy. The Psalms are worship songs and are classified as writings or wisdom literature. Leviticus is law.
The genre is Revelation is harder to pinpoint. Aune discusses J.J. Collins' definition of an apocalyptic; and Collins' definition is based on Revelation. So, Revelation is the proto-type of Apocalyptic literature. Not so, according to other scholars. Some look at particular non-Biblical Jewish works from the 200BC-100AD, and they compile a list of features. Some of those features do not apply to Revelation, so it cannot be an apocalypse.
Aune rejects that conclusion saying that just because Revelation doesn't meet every qualification on the apocalyptic-check list does not disqualify it. Structurally, the majority of verses in Revelation are more like an apocalypse than any other form.
However, Aune also observes that Revelation itself claims to be prophecy (22:18). Furthermore, in apocalyptic literature, the righteous who are persecuted in this life by the wicked are rewarded in the next. And, the wicked who have disregard God in this life and have injured the weak are punished in the next. It seems to be a precursor of 20th century Liberation theology. Prophecy, on the other hand, is a warning to the wicked that they must repent, change. Implicit in this warning is that they will have the opportunity to do so. Revelation is full of such warnings (2:5, 16, 21; 3:3, 19). The opportunity for repentance is a part of the message in Revelation (9:20-21). There is also, and perhaps more often mentioned, reward and punishment. But repentance is not completely missing.
So, Revelation is structured like an apocalypse. In some ways the message suggests prophecy and in Chapter 22 it self-identifies as prophecy. Chapters 1-3 and chapter 22, the beginning and ending, function as a letter. This was a specific 1st century form and Revelation takes that form. So what is the final book of the New Testament, letter, prophecy, apocalypse, or combination of all three?
In my own experience, Revelation is Gospel because in Revelation, I see Jesus and I see who I am supposed to be in Jesus. I see in the four Gospels too, but in Revelation, I meet the Lord in a unique and transforming way. This happened in 1990 when I was called into ministry. It took place again in 2006 when I began the year intending on preaching Revelation every single week of that year (I did not end up doing that, but I hope to someday). And again this year, in April & May, the Lord spoke to me through Revelation after the Lord had thoroughly disrupted my spiritual equilibrium in my journaling through the Gospel of John. As my vision of Jesus keeps expanding in Revelation, I have to call it Gospel. I couldn't make that case in scholarly circles. But from a reflective standpoint I have to. If I ever write a book about Revelation, it will be a reflective piece and I'll call it Revelation as Gospel.