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The explanations given are all excellent. I would merely like to add that hermeneutics is especially applicable when reading and understanding the book of Revelation. John's message to the seven churches was basically that God would ultimately prevail! He uses Old Testament phrases and symbolism that only the intended audience would understand.
If he had spoken more plainly, the Romans would have prevented the letter from reaching its intended audience. There's no telling what would have happened to John.
Since the Romans weren't familiar with the Bible, they probably thought the letter was merely the ramblings of an old man, in exile. But the members of the seven churches knew exactly what hhe meant thanks to the principle of biblical hermeneutics.