For a thousand years in thy sight - Hebrew, “In thy eyes;” that is, It so appears to thee - or, a thousand years so seem to thee, however long they may appear to man. The utmost length to which the life of man has reached - in the case of Methuselah - was nearly a thousand years Genesis 5:27; and the idea here is, that the longest human life, even if it should be lengthened out to a thousand years, would be in the sight of God, or in comparison with his years, but as a single day.
Are but as yesterday when it is past - Margin, “he hath passed them.” The translation in the text, however, best expresses the sense. The reference is to a single day, when we call it to remembrance. However long it may have appeared to us when it was passing, yet when it is gone, and we look back to it, it seems short. So the longest period of human existence appears to God.
And as a watch in the night - This refers to a portion of the night - the original idea having been derived from the practice of dividing the night into portions, during which a watch was placed in a camp. These watches were, of course, relieved at intervals, and the night came to be divided, in accordance with this arrangement, into parts corresponding with these changes. Among the ancient Hebrews there were only three night-watches; the first, mentioned in Lamentations 2:19; the middle, mentioned in Judges 7:19; and the third, mentioned in Exodus 14:24; 1 Samuel 11:11. In later times - the times referred to in the New Testament - there were four such watches, after the manner of the Romans, Mark 13:35. The idea here is not that such a watch in the night would seem to pass quickly, or that it would seem short when it was gone, but that a thousand years seemed to God not only short as a day when it was past, but even as the parts of a day, or the divisions of a night when it was gone.