What does Psalm 90:9 mean?

Humans spend their lives under God's wrath—meaning that humans are persistently sinful and always subject to the judgment of the Lord. Certainly, the generation that disobeyed God in the wilderness languished under His wrath until every member of that generation died, except faithful Caleb and Joshua. Even the faithful, however, still carry the burden of sin and wrongdoing.

Paul informed the Romans that "the wages of sin is death" (Romans 3:23; 6:23). Death comes upon mankind like a sigh: a fading and temporary puff of breath. Nevertheless, there is hope. John 3:36 tells us God's wrath abides on whoever does not obey the Son of God, but "whoever believes in the Son has eternal life." Ephesians 2:4–5 contrasts the life believers enjoy with the death that enveloped them when they were still eternally lost in their sin. God's mercy, love, and grace give believers an endless hope, whereas unbelievers have a hopeless end. Because God had saved him, the apostle Paul could testify, "for to me to live is Christ, and to die is gain" (Philippians 1:21).