The Psalmist makes a distinction between the wicked man and the righteous man in their reaction to being overwhelmed by sin. The wicked man does not call on God and does not think about God, instead choosing to cherish sin in his heart. The Psalmist describes the wicked man as one who does not call on God and does not think about God, instead choosing to cherish sin in his heart because he does not know that the only remedy for sin is to call on the name of the Lord. On the other hand, the righteous man knows that when he is overwhelmed by sin, God will forgive his transgressions. In another place the Psalmist says about his sins that they are more than the number of his hairs and that sin has overtaken him and because of this his heart fails within him. However, despite this, the righteous man still calls on God for help and knows that God will forgive him. So in the Psalms we make a distinction between the reaction of the wicked man and the reaction of the righteous man.  It's likely that the Psalmist is using the awful state of alienation from God as a way to contrast the less wicked man who cherishes sin. The Psalms make a distinction not about each sin, but between pride and humility. And this distinction is talking about the different paths one can take. The reason this verse is so important is because it's the only one in the Psalms that suggests sin isn't fully taken care of by atonement. We need to look at other reasons for him reasoning like this, and figure out what he's really trying to say. So, here the Psalmist is poetically talking to himself and consoling himself that the Lord hears his cries because he does not regard iniquity in his heart because he calls on God. So, he is saying that if he regarded iniquity in his heart, then he would not be able to call on God and thank Him for hearing his prayer. Where as the wicked man has nowhere to take his sin. This shows the difference between hope and hopelessness. If someone were to use this verse to conclude that a Christian could not be accepted on the basis of Christ's work, then it would be like cursing them.