In order for twenty-first century readers to properly understand Revelation, we have to look at it through first century eyes. Their understanding of the book frames our understanding.
Start with the assumption that the last book of the Bible is exactly what it purports to be - a revelation, not a mystery. Add to that assumption the fact that it was written by a first century author and that it was originally read by first century readers who were expected to understand and obey the message contained in it. Take into consideration their first century frame-of-reference and the author's familiarity with the Old Testament. Wrap that all up in the popular "apocalyptic" literary genre of its day with its pervasive use of symbolism. That mixture of elements is what gave rise to the Book of Revelation.