To show that fool's thoughts are always sin, and the scoffer/scorners are hateful to mankind.
Are you a fool? No, fools are unbelievers.
Psalms 14:1 (Amplified Bible)
14:1 To the Chief Musician. [A Psalm] of David. THE [empty-headed] fool has said in his heart, There is no God. They are corrupt, they have done abominable deeds; there is none that does good or right.