Many uses of the phrase "a thousand" in the Old Testament clearly refer to an exact number or round number.
Others are clearly intended as figurative with the meaning of "all," "forever," "many," or "abundantly." This figurative use supports the standard view of amillennialismhaving no literal 1,000 year millennium.
I should mention, in my alternate view of amillennialismthe 1,000 yearsof Revelation 20 is strictly literal;the time from the Resurrection of Jesus to the great schismbetween eastern and western Christendom in 1054 A.D.
Premillennialists base their doctrine of the literal 1,000 year millennium on the six occurrences of the phrase "a thousand years" in Revelation chapter 20.Their justification for doing this is the so-called "literal" hermeneutic in which all passages are interpreted literally unless there are sufficient grounds to interpret it figuratively.
It is common in the Old Testament to interpret this phrase figuratively. A few examples...
He remembers his covenant forever, the word he commanded, for a thousand generations. (1 Chronicles 16:15)
If each generation is about 20 years then a literal interpretation of this verse would yield a time period of 20,000 years in which God remembers his covenant. But there is a contradiction if we do this. In the context, the word "forever" has the same meaning as the phrase "a thousand generations." Thus the phrase "a thousand" is intended to mean "forever."
For every animal of the forest is mine, and the cattle on a thousand hills. (Psalm 50:10)
This passage is not intending to limit God's possession to only the cattle that are on a thousand hills. It is a figure of speech intending to say God owns all the cattle. This is a usage of the phrase "a thousand" (which in this context is clearly a large number) to mean "all." God owns all the cattle.
May the LORD, the God of your fathers, increase you a thousand times and bless you as he has promised! (Deuteronomy 1:11)
This passage is not intending to limit God's blessing to an increase of only one thousand times. Rather it is a figurative way of saying God is the source of "all" increase and "all" blessing.
How could one man chase a thousand, or two put ten thousand to flight, unless their Rock had sold them, unless the LORD had given them up? (Deuteronomy 32:30)
The phrase "a thousand" is not intended to represent an exact number but, rather merely a large number.
Even if he lives a thousand years twice over but fails to enjoy his prosperity. Do not all go to the same place? (Ecclesiastes 6:6)
Clearly a figure of speech since people have never lived 2,000 years.
But do not forget this one thing, dear friends: With the Lord a day is like a thousand years, and a thousand years are like a day. (2 Peter 3:8)
This verse is usually used to support the idea each day of the creation week corresponds to 1,000 years of human history. But actually, that is an incorrect interpretation. In the context, this passage is saying that 1,000 years (a long time to us humans) is like a day to God. So it's not "1 day = 1,000 years," instead it's "1,000 years (of human time) = 1 day (to God)."
For a thousand years in your sight are like a day that has just gone by, or like a watch in the night. (Psalm 90:4)
Very much like the passage above.
The 1,000 years began sometime with Jesus: when he proclaimed himself king in the triumphal entry into Jerusalem, or at his crucifixion, or at his resurrection.
Regarding the great schism between east and west: at some point the western church started using the filioque clause in the Nicene Creed which was very distressing to the eastern church and was an important cause of the split. Two notable events regarding the filioque which occurred about 1,000 years after events in the life of Jesus...
Before the time of Satan's release, he perhaps could have destroyed Christianity. But after his release, Christian doctrine was too entrenched to ever be destroyed, although he continues to try to destroy it.