The Bible is very literal and should, as most other texts, be read literally unless the context tells us otherwise. The book of Revelation is no different. The various images and pictures found in Revelation, if required to be taken non-literally, are all explained in the passage where they occur or elsewhere in the Bible. Nowhere are the periods of time shown to be non-literal periods. Those that do not believe in the literal 1000 year millennial period either have a false doctrine on Israel (they falsely believe the Church inherits the blessings of Israel, and therefore have substituted Israel – rarely do they believe they also also inherit the cursing – see Deuteronomy 28:14-68), or decide that numbers have some other meaning than their literal meaning without any indication that this is so. These are simply not true. Nowhere does the Bible allegorise periods of time unless clearly stated. Daniel found this when reading Jeremiah's prophecy – 70 years meant 70 years! In Revelation we have periods of time mentioned at least four times; 1260 days in 11:3, 3½ days in 11:9 & 11, 1260 days in 12:6, and 1000 years in 20:2, 4, 5, 6 & 7. These all relate to a defined numeric period of time, and cannot be allegorised to mean anything else.
The main issue is that Revelation Chapter 20 is not the only, or indeed the main passage, that provides details of the 1000 year millennial period. Indeed most of the events in Revelation have been explained in the Old Testament, hence nearly 800 times is the Old Testament eluded to in the Revelation. What is unknown in the Old Testament and the gospels is the order of the events or the timing of the events. Revelation chapter 20 gives the length of time of the millennial reign, the time it will occur along with one other piece of information not found in the Old Testament – the occasion of the ending of the millennial reign.
Evidence of the literal millennial reign is found in the covenants God made with Israel. Most of these are unfulfilled to this point in time, but will be fulfilled in a messianic kingdom of the millennial period. Complementing the covenants of God are the prophecies made to Judah and Israel that speak of a Messianic Kingdom that will occur in the millennial period. The covenants are:
Therefore, there will be a millennial reign of 1000 years where the Messianic Kingdom will be established, and Jesus the Messiah will be the King of the Gentiles and the Jews.