I’d like to suggest an alternative to the common understanding of a well-known verse. Verse 12 of Psalm 90 is translated: “So teach us to number our days that we may get a heart of wisdom” (ESV).
The verse is usually taken as a prayer for God to give us the wisdom that comes from considering the brevity of our lives. Spurgeon’s comments on the verse spell out the contents of the wisdom: “Men are led by reflections upon the brevity of time to give their earnest attention to eternal things.” And, “We have not enough time at our disposal to justify us in misspending a single quarter of an hour.”
Prayer for wisdom is certainly encouraged in the Bible, and wisdom certainly includes living in light of eternity and making the most of each day. So the common understanding of this verse makes it a sensible prayer.
However, the common understanding is hard to support when the verse is considered in context. Psalm 90 is not asking for a change in the mindset of the person praying; it’s asking for a change in God’s treatment of humans. The following verse cries out to God: “Turn, O LORD! How Long? Have Pity on your servants!” (13) The psalmist prays that God would turn his wrathful aspect away from his people and turn toward them show his favor and steadfast love (14, 17).
The psalm’s references to the brevity of human life are part of its distinctive argument for divine mercy. The psalmist begins by reminding God of the difference between him and mortals in regard to their lifespans. “From everlasting to everlasting you are God,” he says (2). “A thousand days in your sight are but as yesterday when it is past” (4). Humans, in contrast, are as short-lived as grass: “in the morning it flourishes and is renewed, in the evening it fades and withers”(5-6).
The difference between the everlasting God and the short-lived mortals becomes a problem when human sin incurs God’s wrath. The psalmist asks God, who may think his “anger is but for a moment” (30:5), to consider that from the human perspective it seem to be life-long: “All our days pass away under your wrath” (9). In an old joke, a man says to God “If a thousand years to you are like a day, then million dollars must be like a penny. Could I have a penny?” God replies, “Sure. Just a minute.” The psalmist’s point is that God’s wrath for even one of his minutes is too much for a human to bear.
In the conclusion of the psalm, the psalmist makes an unusual request: “Make us glad for as many days as you have afflicted us, for as many years as we have seen evil” (15). He doesn’t deny our sinfulness, or the justice of God’s wrath. All he’s asking is that we could have as many years of God’s favor as we’ve had of his wrath. Earlier he makes his well-known estimate that “the years of our life are seventy, or by reason of strength eighty” (10). In his simple calculation, if a human is going to have a life that’s not half bad, God is going to have to turn from wrath to favor by age 35, or 40 at the latest.