"While the day of the Lord certainly has a chronological reality to it, the day of the Lord is first and foremost a state of being, a state of illumination, understanding, knowledge, consciousness, and experience. The day of the Lord is the garden of Eden, it’s the sabbath of God, it’s the cessation of the flesh, and the strivings, desires, and anxieties of the carnal mind. It’s the ceasing of trying by soulish strength to think up and work up the nature, will, ways, and purposes of God, and it’s entering instead into the power of His life, light, and glory. It’s the discovering and unveiling of the Christ within! That’s what John discovered in Revelation 20:1-6. He discovered the Most Holy Place. There is a people on the earth today that is beginning to experience the reality and fulfillment of all that the prophets prophesied of through the ages. The third day, the third feast of Israel, and the third realm in God are all pre-figured by the Most Holy Place in the tabernacle of Moses with its dimensions of ten cubits wide, ten cubits long, and ten cubits high — one thousand cubits square! Those dimensions correspond precisely with the “thousand years” of John’s vision, for one thousand is a figure composed of 10 X 10 X 10. Beyond the veil, in the Most Holy Place, the one thousand cubits point to the one thousand years of the reign of God’s elect upon the thrones of judgment. Both measurements are symbolisms representing the reign of Christ and all the holy sons of God in the power of the kingdom of God and the brightness of the day of the Lord!"
Much more in the link:
https://www.godfire.net/eby/rev218.html
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"The figure ten is a symbol of earthly completeness, so ten times ten times ten, the cube of ten, or a thousand, is merely a symbol of multiple completeness or fullness."