The defining feature of Revelation 20 is the “thousand years,” mentioned six times in the chapter (vv. 2, 3, 4, 5, 6, 7). Theologians have labeled this thousand year period as the “Millennium” (mille = 1000; anne = year).
The church has had difficulty assimilating the Millennium as described in Revelation 20 with what the rest of Scripture says about eschatology.
Historically, most Reformed churches have concluded that the Millennium is roughly equivalent to the church age. The Millennium starts with the first coming of Christ and ends with the second coming of Christ. Thus, the Millennium spans the gap between the two comings of Jesus Christ.
This means that the Millennium is now almost two thousand years long (and counting). Some have been troubled by this, expecting the Millennium to be exactly one thousand years long. While this is certainly a plausible expectation, Scripture often uses large numbers in a generic or symbolic sense.
“Then I looked, and I heard the voice of many angels around the throne, the living creatures, and the elders; and the number of them was ten thousand times ten thousand, and thousands of thousands” (Revelation 5:11).
The word for “ten thousand” is myriad. A myriad can refer to the exact quantity of ten thousand, but it is also used to refer to an inexact large number, so much so that lexicons include “countless thousands” as a frequent translation.
The word for “thousand” is chilias, from which we get kilo, as in a kilogram. Likewise, the word chilias can refer to exactly one thousand, but it is also used to refer to an inexact large number. We see this use of “a thousand” in the Scriptures.
“For every beast of the forest is Mine, And the cattle on a thousand hills” (Psalm 50:10).
God is not limiting his possession of cattle to exactly one thousand hills, but using a thousand in a generically large sense. God owns the cattle on every hill, which would actually be a much larger number than one thousand hills, probably in the millions.
“For a day in Your courts is better than a thousand outside. I would rather stand at the threshold of the house of my God Than dwell in the tents of wickedness” (Psalm 84:10).
David is not making an mathematical equation to say that one day with God is better than exactly one thousand days without God. David is saying that one day with God is better than any number of days without God.
“For a thousand years in Your sight Are like yesterday when it is past, And like a watch in the night” (Psalm 90:4).
“But, beloved, do not forget this one thing, that with the Lord one day is as a thousand years, and a thousand years as one day” (2 Peter 3:8).
When Peter alludes to Psalm 90, he is not employing a precise, algebraic formula. He is simply illustrating that God is not bounded by time.
We ought to bear these examples in mind when we come to Revelation 20, because John is not writing about a period of “one” thousand years. The word “one” is not in the Greek text. John writes about “a” thousand years. Such intentional imprecision indicates that this “thousand years” is probably a generically large number, just like “the cattle on a thousand hills” or “a thousand days outside.”
This squares with the rest of the Scriptures. If the Millennium was exactly one thousand years long, then we could know exactly when it was coming to an end.
On the other hand, if the Millennium is a generically large length of time, then we do not know exactly when it ends. This is true of the second coming of Christ. We do not know when Christ will return, which is how we are supposed to live.