Thomas Aquinas on "the fool's" reasons

In his interpretation of the first verse of Psalm 13 (14), Saint Thomas refers to Saint Anselm who had claimed that those who deny God's existence are fool" because they try to think what is unthinkable. In the light of Aristotle's theory of science and considering how Anselm's argument had been used by Saint Bonaventure, Saint Thomas asks whether God's existence is immediately known. He argues that this is not the case: to know God, human beings have to search for the cause of things. However, those who are content with using things without even trying to inquire about their causes are fool".