What does Psalm 39:5 mean?

David knew life is short, so there's no reason to spend it in despair. In this case, he was struggling with frustration and a desire to speak out about wicked people (Psalm 39:1–3). When he felt the need to speak up, he did so by praying to ask God for humility (Psalm 39:4). David asks God for a reminder of his own limited lifespan—to be assured that his problems and concerns were nothing compared to the power of God. Rather than being aggravated by his situation, David asked God to alter his perspective, so he could see things in a more godly way.

A "handbreadth" was the measure of four fingers; about the distance across the palm. Compared to God's eternal existence, a human lifetime is a mere breath (James 4:13–15). In his prayer, Psalm 90, Moses reflected on life's brevity. He referred to a lifetime in his day as seventy years or eighty if a person was strong, and he recognized that the years "are soon gone, and we fly away" (Psalm 90:10). Like Moses and David, Job pondered the brevity of life. He commented in Job 7:6, "My days are swifter than a weaver's shuttle." In verse 16 he compared his life to a breath. David's wise son Solomon also commented on life's brevity. He said, "For who knows what is good for man while he lives the few days of his vain life, which he passes like a shadow?" (Ecclesiastes 6:12).