Calvin’s observations on Psalm 14:1 are worth re-hearing:
As the Hebrew word נבל, nabal, signifies not only a fool, but also a perverse, vile, and contemptible person, it would not have been unsuitable to have translated it so in this place; yet I am content to follow the more generally received interpretation, which is, that all profane persons, who have cast off all fear of God and abandoned themselves to iniquity, are convicted of madness.
David does not bring against his enemies the charge of common foolishness, but rather inveighs against the folly and insane hardihood of those whom the world accounts eminent for their wisdom. We commonly see that those who, in the estimation both of themselves and of others, highly excel in sagacity and wisdom, employ their cunning in laying snares, and exercise the ingenuity of their minds in despising and mocking God.
It is therefore important for us, in the first place, to know, that however much the world applaud these crafty and scoffing characters, who allow themselves to indulge to any extent in wickedness, yet the Holy Spirit condemns them as being fools; for there is no stupidity more brutish than forgetfulness of God.