The greatest enemy of God in Scripture is Satan. He is the dragon, the serpent who has waged war against God from of old. He and the other fallen angels (the demons) are not atheists. They know God exists, and they hate God. Because they hate God, their entire existence is one of defying God. And here is where we see something worse than atheism.
It is one thing to deny the existence of God. This is what fools do. It is another thing to defy the God whose existence you know. This is what Satan and the demons do.
Defying God is worse than denying God, and this is what we do every time we sin against God. When we sin against the God we know exists, we are defying God and engaging in behavior that is fundamentally satanic in nature. We are doing what the demons do.
This is important because we as Christians can often behave in a Pharisaical manner, looking at the atheist and saying, “God, I thank You that I am not like them.” What we fail to realize is the utter wickedness and evil of what we are doing when we sin, when we defy God.
The fool says in his heart, “There is no God.”
The believer who sins says in his heart, “No!” to God.
We are not without hope, however, for there is good news. There is the gospel. Jesus Christ died for our sins (1 Cor. 15:3), and “If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness” (1 John 1:9). The Lord Jesus now intercedes for us at the right hand of God (Rom. 8:34).
If you have defied God, if you are defying God, repent and turn to Jesus Christ, the only One in whom forgiveness for sin may be found.