Perhaps only Isaiah 40 can compare with this psalm in presenting God's grandeur and eternity in contrast to our frailty and mortality. Moses' point, however, is that God's eternity is the answer to our problem with time.
One might think that we hardly need to be reminded of this. But when the misconception that we are already immortal ("You shall not surely die") is combined with our innate and powerful proclivity toward abusing time, it is urgently necessary that God emphasize this on occasion.
God often underscores the brevity of our lives. Job laments: "Now my days are swifter than a runner; they flee away, they see no good. They pass by like swift ships, like an eagle swooping on its prey" (Job 9:25-26). In Psalm 39:4-5, David prays:
LORD, make me to know my end, and what is the measure of my days, that I may know how frail I am. Indeed, you have made my days as handbreadths, and my age is as nothing before You; certainly every man at his best state is but vapor. Selah.
And finally Asaph writes, "For He remembered that they were but flesh, a breath that passes away and does not come again" (Psalm 78:39).
The rapid passage of time is something we need to be serious about. We cannot live as though there is no day of reckoning because judgment is now upon the household of God (I Peter 4:17).