You see, it is a characteristic of Christians to regard the Scriptures as the true, infallible Word of God. When they are in need of comfort themselves, they find none. They cry for mercy; they fall on their knees; they plead to God. God made David taste the bitterness of sin. As such, we notice that, after his fall, David is generally more often sad than joyful and that one misfortune after another happens to him.
God permitted these misfortunes to afflict David to keep him from falling into yet another sin-not because he had not forgiven his sin. It was God’s love and mercy that prompted Him to act like this. Of course, someone still dead in sin would probably still think: “Why was David so foolish as to torture himself with a sin that had been forgiven by God?” People reasoning this way turn the Gospel into a pillow for their carnal minds to rest upon. They keep on living in sin, imagining they will end up in heaven anyway. This kind of Gospel is a gospel for the flesh.
Law & Gospel: How to Read and Apply the Bible by C. F. W. Walther (A Reader’s Edition) p 50