Both Psalm 14:1 and Psalm 53:1 read, “The fool says in his heart, ‘There is no God.’”
Some take these verses to mean that atheists are stupid, i.e., lacking intelligence. However, that is not the only meaning of the Hebrew word translated “fool.” In this text, the Hebrew word is nabal, which often refers to an impious person who has no perception of ethical or religious truth.
The meaning of the text is not “unintelligent people do not believe in God.” Rather, the meaning of the text is “sinful people do not believe in God.” In other words, it is a wicked thing to deny God, and a denial of God is often accompanied by a wicked lifestyle.
The verse goes on to list some other characteristics of the irreligious: “They are corrupt; their deeds are vile; / there is no one who does good.” Psalm 14 is a study on the universal depravity of mankind.
Many atheists are very intelligent. It is not intelligence, or a lack thereof, that leads a person to reject belief in God. It is a lack of righteousness that leads a person to reject belief in God.
Many people do not object to the idea of a Creator, as long as that Creator minds His own business and leaves them alone. What people reject is the idea of a Creator who demands morality from His creation. Rather than struggle against a guilty conscience, some people reject the idea of God altogether. Psalm 14:1 calls this type of person a “fool.”