What the Bible is saying is that one who does not believe is both stupid and blind. He does not see what there is to see. Not only is he blind, but he is also likely to act blindly. He does not recognize any purpose in existence, and is therefore likely to act without direction. He does not recognize Truth, and is apt to do everything wrong. He is so unperceptive that he cannot be trusted. He says that there is no God because he is a fool. He is too blind to see God all around him; or else he is too selfish to share his own world with its Creator.

In the entire Bible, you will not find a single philosophical argument for the existence of God. It is simply assumed. The Bible does not waste time trying to convince the atheist that he is wrong. He is considered a fool, too dull to understand, or too wicked to want to.