Only fools say in their hearts, "There is no God."

Though many people may have great brains and may know a number of things, they may still be governed by their lusts and passions and desires, and that is why they are fools. They want to live the kind of life that the psalmist describes here. "They are altogether become filthy," he says. "There is none that doeth good" (v. 3). It is because they want to be filthy that they say, "There is no God."

- D. Martyn Lloyd-Jones, excerpt from sermon entitled, "The Folly of Unbelief"

Cross References to Psalm 53:1

Romans 3:10
As it is written: "There is no one righteous, not even one;

Psalm 10:4
In his pride the wicked man does not seek him; in all his thoughts there is no room for God.

Psalm 14:1
For the director of music. Of David. The fool says in his heart, 

"There is no God." They are corrupt, their deeds are vile; there is no one who does good.

Psalm 74:18
Remember how the enemy has mocked you, LORD, how foolish people have reviled your name.

Psalm 74:22
Rise up, O God, and defend your cause; remember how fools mock you 
all day long.