Someone asked me a question on the 7 letters to the 7 churches in Revelation – how do people know that each church is representative of a church age in our history?
The opinion that each of the 7 churches represents a phase in Church history came from comparing what the letters say with actual events in the life of the Church. This was only discovered with hindsight, but the specific churches the Lord chose to address and the order in which He did so was unusual enough to arouse the curiosity of scholars.
What they discovered is that the letters provide an accurate historical summary of the last 2000 years, and a realistic prophecy of the time left before the 2nd Coming. This is especially interesting when you see Thyatira as the Catholic Church and notice that some are promised to be taken in the rapture while others will be left behind, Sardis as the main line protestants, where the same is true, Philadelphia as the born-again evangelical church where all will be taken, and Laodicea as the apostate church where all will be left behind.