Ps. 14:1 Only fools say in their hearts, "There is no God." They are corrupt and their actions are evil, no one does good!
It is interesting just how foolish people can be. Mankind will do just about anything to avoid believing in God. I believe it is because they do not want to deal with the possibility of consequences for sin. As long as people deny there is God, they can live with sin without all the guilt and shame, or so they think. One cannot believe in God in his heart without knowing the guilt and shame that comes from living in sin.
The problem most people have who claim to believe in God is that their belief never gets from their head to their heart. I believe it's equally foolish to believe only with the head as it is to believe there is no God. Those who only believe with their minds live corrupt lives, their actions are evil, they do no good. We must never forget that all the demonic forces of hell have a head knowledge of God. In fact, hell will be full of people who believe in God. There will be no atheists in hell.
Likewise, foolish are those who believe in their hearts that God is and live like He isn't. In order to do it, one must deny there is a hell. God must be perceived as only a god of love who will accept everyone into His kingdom. Such belief is based on nothing but lies. God is both holy and love. He cannot be one without the other. One born in grace does not have a license to sin.
When we leave, or kick, God out of our hearts, we become slaves to sin and bear the consequences of it. Believe in your heart that God is and live like it and you will make it home to heaven.