The fool says in his heart, “There is no God.” They are corrupt, they do abominable deeds, there is none who does good.
There is nothing new about not believing in God; it is the oldest thing in the world to deny Him. This is what I find so pathetic, that people think it is clever not to believe in God, that it is modern, that it is something new, that it is something wonderful! But here is a man, King David, writing all this a thousand years before Christ-nearly three thousand years ago-and there were people saying then, “There is no God”-just what clever people are saying today, those who try to argue that they are saying it in terms of some latest esoteric knowledge that they have been given and that other people still do not have. But is it not clear that this has nothing at all to do with knowledge as such?
No; it is a question of understanding, and that is a very different thing. Men and women may have a lot of book knowledge, but that does not mean they have understanding or that they have wisdom. They can be aware of many facts, but they may be fools in their own personal lives. Have we not known such people? I have known men in some of the learned professions; I would take their opinion without a moment’s hesitation because of their knowledge and because of their learning. But sometimes I have known some of those men to be utter fools in their own personal lives. I mean by that, they behaved like lunatics, as if they had not a brain at all. They have behaved in exactly the same way as a man who never had their educational advantages and who had none of their great knowledge. They drank too much even as a less educated man did; they were guilty of adultery even as he was.
There is all the difference in the world between knowledge-an awareness of facts-and wisdom and real understanding. Though 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.” So there is my first reason for calling such people fools. They are men and women who listen to their hearts, their desires; they are governed by what they want to do rather than by true understanding.
D. Martyn Lloyd-Jones, Seeking the Face of God: Nine Reflections on the Psalms (Kindle Edition)