So teach us to number our days
that we may get a heart of wisdom.
This is a prayer that Moses prayed. It is literally timeless. It begins with an acknowledgement of God's love for humanity that spans generations and lifetimes (Psalm 90:1). It then acknowledges God's own timeless eternality (Psalm 90:2-4). And very quickly our own short mortality is a theme of the Psalm (Psalm 90:3, 5-6). The reason this is our lot is because of the consequences of our sin (Psalm 90:7-8).
Since our lives are limited with a beginning and an end, HOW we live is the most important thing. Moses prayed that we might number our days to gain wisdom. We might live 80 years... but eventually we all must answer to our Maker (Psalm 90:10-11).
What matters in our lives is God. He has pity on us (Psalm 90:13). God's faithful love satisfies us for every one of our all too brief days (Psalm 90:14). God brings us joy and gladness (Psalm 90:14-15). God's power and favor mark the lives of those who have learned to number their days for His glory (Psalm 90:16-17), and that is the best way to live.