For several years now my Father and I have been doing a yearly Bible reading plan; we just finished 2012. The plan for 2012 was to read through all of the Apostle John's writings: The Gospel according to John, 1st, 2nd and 3rd Epistle of John and The Revelation of John. Reading the last chapter of Revelation is such a great conclusion to our reading plan, the year, the book, and The Book. Among the very recapitulative passages of chapter 22 are v7, vv10-11, vv12-15, vv17 & 20, & vv18-19.
"He also said to me, “Don’t seal the prophetic words of this book, because the time is near. Let the unrighteous go on in unrighteousness; let the filthy go on being made filthy; let the righteous go on in righteousness; and let the holy go on being made holy.”"--Revelation of John 22:10-11
The passage that stands out and can be most easily misunderstood is the one quoted at the top: 22:10-11. One thing that people find perplexing in this passage is the first part of the parallel--the parallel being made up of the unrighteous/filthy with the righteous/holy. We can see plainly throughout the entirety of scripture that we are called to be holy, but when are we called to be filthy (or unclean in the OT)? We are called to not be filthy, in fact, repeatedly. Well, as always, the way we deal with mystifying portions of the holy writ is by dealing with the context.
As I've referenced above, the context of chapter 22 (spec. vv 6-20) is that of conclusion--it brings about the culmination of all of Revelation. The passages I listed above are, like so many of the NT epistles, answering the question, "In light of these things how shall we now live?" The Book of Revelation was written to the first century universal church and specifically to seven churches written to directly. The rest of Revelation spends its time warning the saints about coming distractions, including persecution, temptation of idolatry, and temptation of 'love of the world', and comforting them with the hope of the knowledge of their security in salvation, in perseverance, and exclusion of certain persecution. Along with this important context is the context of the other concluding verses. Among these are some with Jesus saying that He is coming quickly and that the time is near, some telling the believers to say, "Come!", and, it seems, John himself adds, "Come, Lord Jesus!" So, we see two major themes in this context: 1) the state of the world as it is and will be, as told by The Lord 2) the answer to the way things are and will be, as told by The Lord.
The state of things and things to come in Revelation are represented by plagues, which is a revelation from God (i.e., these things will happen), and the answer to these things is Jesus arrival. So, what we pray, as directed in this chapter, is, along with John, "Come, Lord Jesus!"; what we shouldn't pray is, "Your will not be done", against His sovereignty. That is what I think this passage is getting at: 'I'm telling you what will happen, not what may happen. So, do not attempt to change the sate of the world or the state of mankind. Pray that I come quickly. But, you, persevere. Let those whom I have made for destruction keep on being unholy, but, you, keep on being holy, for I have made you for glory. I will change those whom I will by the preaching of the word. Pray that I will come and proclaim My Gospel.' That's what I think it means.