Commentators universally agree that this verse contrasts God's eternal nature with our finite experience of time. A thousand years, an immense span for humanity, is compared to a fleeting moment for God—like a day that has already passed or a brief watch in the night. This isn't a mathematical equation but a poetic way to grasp the concept of God's timelessness, where past, present, and future are all present to Him in an 'eternal Now,' as Charles Spurgeon describes it.