I think that the letters to the seven churches were written before the Romans and Jews went to war in 66 CE. I think that Revelation chapter 12 tells the story of how John got to Patmos. It tells of the remnant of Israel in exile, (Gen. 37:9-10, Micah 4:9-10) being oppressed by Gentile empires (the dragon), and being persecuted for their faith (Dan. 8:10-11) by Antiochus IV Epiphanes. She gave birth to the Messiah, whom was caught up to heaven. After that, she (the elect remnant) fled to the wilderness (outside the country, to the Gentiles.) Then the dragon makes war in heaven, which on earth looks like the Romans persecuting the disciples specifically, calling them Christians. (Rev. 12:10-11)
It shows that they overcame Satan by the blood of the Lamb and did not love their lives even unto death. This is the first time Satan is mentioned in the book. What it is actually doing is referring back to Job, where Satan tempts Job by sending him all kinds of plagues to get try to get him to curse God. But Job remains faithful. In the same fashion, the disciples were being persecuted for their faith throughout the empire, and even in Rome, but they remained faithful.
So, John was on Patmos Island because he remained faithful to Christ. It seems like the Romans had found all the leaders of the Church and either killed them (like Peter and Paul) or were about to kill them (like John; Matthew 20:20-23.) Revelation 12 also shows that, after the persecution had ended, the dragon pursued the woman by means of a flood. Here, the serpent is used, and then the dragon. The use of the word serpent looks back to the Garden of Eden, concerning cunning deception. In this case, false prophets and false christs made their way throughout Judea, trying to rally support for the war against Rome. At this point, the elect (144,000 sealed) fled Judea as Jesus told them to (Luke 21:20-21) and brought the Gospel to the Gentiles. That is the significance of the seven churches of Asia-Minor: They were the places the elect fled to.
So the messages to the seven churches were messages to the elect and those that came to believe in Jesus because of them.
Notice that in Revelation 1:3, John says: "Blessed is he that readeth, and they that hear the words of this prophecy, and keep those things which are written therein: for the time is at hand."
What was about to happen was that Judea was going to go to war with Rome. John was given these messages on Patmos Island to send out to the disciples at the seven churches encouraging them to obey Christ's commands (despite Judaizers) and hold to the testimony of Jesus' salvation (despite Caesar.) The end of the Jewish nation was at hand, and the elect needed to know about it and to be prepared to be persecuted for not joining along. At the same time, the Times of the Gentiles were at hand, so the newer converts needed to know what they would face in the future for their faith (Revelation 12:17, chapter 13.)
That's my take on it.