“Before the mountains were born or you brought forth the whole world, from everlasting to everlasting you are God. A thousand years in your sight are like a day that has just gone by, or like a watch in the night.” Psalm 90:2,4
The phrase “mountains … world” is a description using repetition to emphasize that the everlasting God made all things. Everlasting (or eternity) is defined as having no beginning and no end.
The term “thousand years” is simply a recognition that God is beyond time. The Psalmist is merely contrasting God’s permanence with human life. From God’s perspective, a thousand years is fleeting.
Some rabbis later concluded that God had a “day” that lasted a thousand years. This conclusion led to speculation and computation about the ages of the earth and God’s timing for Judgment Day. However, such speculation cannot be based on this text. An early church author put it this way, “No one may imagine a thousand years are reckoned by God as one day, as if with God days were so long, when this is only said in contempt of the extent of time: he adds, ‘and as a watch in the night:’ which only lasts three hours”.
The repetitious description “watch in the night” suggests sleep, where there is no sense of time passing.
God’s blessings on your day…