Psalm 90 bears the title, A Prayer by Moses, the man of God. It opens Book IV of the Psalter and is the only psalm attributed to Moses. It contrasts God's eternity with human frailty. Lord, you have been our dwelling place for all generations. Before the mountains were born, before you had formed the earth and the world, even from everlasting to everlasting, you are God. God is not only eternal but also a home for his people.
Human life, by contrast, is brief. You turn man to destruction, saying, Return, you children of men. A thousand years in your sight are just like yesterday when it is past, like a watch in the night. In the New Testament, Peter applies this to the timing of the Lord's return (2 Peter 3:8). People are like grass that sprouts in the morning and withers by evening. Moses connects this frailty with sin: You have set our iniquities before you, our secret sins in the light of your presence.
The response is not despair but prayer. So teach us to count our days, that we may gain a heart of wisdom. Moses asks God to relent, to satisfy us in the morning with his loving kindness, and to make us glad for as many days as we have been afflicted. The final request gives lasting meaning to short lives: Let the favor of the Lord our God be on us. Establish the work of our hands for us. Yes, establish the work of our hands.