BUT, lest the above reflection provide a pretext for pride, consider: in your natural state (Eph 2:3) YOU are a fool as well. Apart from the grace of God, we ALL are fools.
Psalm 14 begins with the phrase, "The fool says in his heart, 'There is no God'." Note that it does NOT say, 'The fool says in his mind...' It does not seem that this Psalm is written primarily as a polemic against a philosophical movement. A person may say "There is no God" in his or her heart even if he or she would never dream of saying this statement aloud. A person may say "There is no God" in his or her heart even if he or she never thinks these exact words. This is because the heart of sinful people is bent against God: sinners desire fleeting pleasures and self-recognition, and do not submit to God and seek God's glory.
AGAIN: Psalm 14 is NOT just directed against people who would call themselves atheists. This is evident even from the end of Psalm 14:1, "There is no one who does good." This idea is further developed in verses 2-3:
2 The Lord looks down from heaven
on the sons of men
to see if there are any who understand,
any who seek God.
3 All have turned aside,
they have together become corrupt;
there is no one who does good,
not even one. (NIV 1984)
(These exact words are picked up by the Apostle Paul in Romans 3:10-11 as he argues that all people are under God's judgment due to their sin.)
In our natural state (Eph 2:3): who understands spiritual matters? The answer comes: "No one." Who seeks God? "No one." Who does good? "No one... not even one." On the other hand, "All have turned aside; they have together become corrupt."
And even believers-- those who have been rescued from this natural state by the Holy Spirit-- when we sin, we act as if there is no God: we act like fools.
Reflecting on Psalm 14 should make us cry out for a Savior. Indeed, note that this Psalm ends with a cry for salvation:
Oh, that salvation for Israel would come out of Zion!
When the Lord restores the fortunes of his people,
let Jacob rejoice and Israel be glad!
This is the good news of the Christian faith: as Jesus suffered and died on the Cross, the One who is Wisdom took on the penalty for our willful ignorance; the Savior took on the penalty for our defiant lostness; the One who is Good took on the penalty for our badness; the One who always did the will of His Father took on the penalty for our straying; the One who is perfectly pure took on the penalty for our vile corruption of morals and conscience. Jesus rose from the dead-- showing that He is victorious over sin, death, and Hell-- and now He lives, offering eternal life to all who turn from their sins and believe in Him.
Trust in Him today.