What does Psalm 53:1 mean?
Use of the term "fool" here does not necessarily mean a person is unintelligent. Rather, it means that this particular choice is irrational, unwise, or ridiculous. Jesus told a story about a rich farmer whose land produced abundant crops. He decided to build bigger barns to accommodate the bumper crops, and he told his soul to take life easy. "Relax, eat, drink, be merry," he said to his soul (Luke 12:19). He may have been a smart and capable farmer, but God called him a fool because he valued material possessions instead of God. God said to him: "Fool! This night your soul is required of you, and the things you have prepared, whose will they be?" (Luke 12:20).It is because the fool rejects God that his life is corrupt and his iniquity is abominable. Without the admission that God exists, the fool does not respect God's laws, so he leads a lawless life. His life is sinful and lacks any moral goodness. Worse, denial of God's existence leads to the assumption that humanity is free to define right and wrong according to their own preferences. That eventually leads to a "might makes right" approach that excuses atrocities.
Whoever denies God is sure to worship a false god. Some fools worship themselves or a celebrity or wealth or fame.