One of the things that keeps coming up in my mind is the question of why the Revelation would be addressed to seven churches in Asia, rather than to every church everywhere, or to the churches in Judea.
There have been several explanations offered for why John addressed the seven churches.
1.) Some have suggested that he actually wrote at such an early date that there were only seven churches in Asia. I don’t personally ascribe to this, but, it is an interesting thought.
2.) I think that the more appropriate answer is that since the book tells us right up front that it is a book of symbolism, that the seven churches are symbols, or representatives, of the church at large, as it existed at the time.
As in Paul’s writings, he instructed that his epistles be read in all the churches, we can be sure that this happened with the Apocalypse as well. Thus, the principle of "if the shoe fits, wear it" would have applied to those churches outside of Asia. If the church in Rome for instance, was guilty of losing her first love, then the admonition to the church at Ephesus would have been applicable.
There are clearly some distinctive, applicable only to the specific situations in the seven churches, and that is one of the reasons why we must honor the time element in the letters, and the spefic language that addressed those specific churches.
With that said, when the church at Pergamos was castigated for allowing the teaching of "Balaam" that consisted of sexual immorality and the eating of meats sacrificed to idols, we hopefully see here the echoes of Romans 14, 1 Corinthians 6, 8, 10, and a wider problem within the church throughout the empire.
So, there were both specific and generic issues dealt with as the Spirit addressed the churches.
One other thing, and that is as Jesus addressed the churches, the sense of imminence of the end permeates virtually every letter. This comports precisely with the opening of the letter and the close, that the prophecy was about to be fulfilled.
In conjunction with the imminence, we find that the promises of victory and reward promised to each of the churches, if they remained faithful, are the very promises that were to be brought at the parousia. This fact emphasizes not only the imminence but the first century applicability of the parousia promises.