Adam Clarke's Commentary on the Bible

Verse 1 (Psalms 14:1)

The fool hath said in his heart, There is no God - נבל nabal , which we render fool, signifies an empty fellow, a contemptible person, a villain. One who has a muddy head and an unclean heart; and, in his darkness and folly, says in his heart, "There is no God." "And none," says one, "but a fool would say so." The word is not to be taken in the strict sense in which we use the term atheist, that is, one who denies the being of a God, or confounds him with matter. 1. There have been some, not many, who have denied the existence of God. 2. There are others who, without absolutely denying the Divine existence, deny his providence; that is, they acknowledge a Being of infinite power, etc., but give him nothing to do, and no world to govern. 3. There are others, and they are very numerous, who, while they profess to acknowledge both, deny them in their heart, and live as if they were persuaded there was no God either to punish or reward.

They are corrupt - They are in a state of putrescence and they have done abominable works - the corruption of their hearts extends itself through all the actions of their lives. They are a plague of the most deadly kind; propagate nothing but destruction; and, like their father the devil, spread far and wide the contagion of sin and death. Not one of them does good. He cannot, for he has no Divine influence, and he denies that such can be received.

- Adam Clarke's Commentary on the Bible