The second striking thing in these opening verses, which comes together with the first, is David's profound awareness of his sin and its true nature. In verse one he used three words to describe God's compassion. In verse two he uses three corresponding words to describe his sin.

David's sin, in which he committed adultery with Bathsheba and later, after discovering that she was pregnant, arranged to have her husband Uriah killed in battle, is the dark background for the psalm (see 2 Sam. 11, 12). But this very blackness led David to the light.

A person who does not have much experience studying the Bible is likely to think that a well-known passage must be easy to elaborate. "It must be easy to teach John 3:16, the twenty-third Psalm or the Christmas story,” he might say. Actually, the well-known passages are the hardest, and some seem almost impossible to expound.

"You shall not commit adultery” (v. 18). The second reference is to the seventh of the Ten Commandments, found in Exodus 20:14 and Deuteronomy 5:18. It concerns sexual relations with another person's wife or husband. But it is also broader than that, since it embraces all kinds of sexual sins, including the outward sin of fornication and the inner sins of impure thoughts or lust. Jesus said that "anyone who looks at a woman lustfully has already committed adultery with her in his heart" (Matt. 5:28).

With verse 16 there is an unmistakable movement to a second class of people, since the verse begins, "But to the wicked, God says." However, it is important to see that even here we are not in the presence of the heathen but rather still with the alleged people of God. Derek Kidner calls these "the nominally orthodox," "hypocrites" and "hardened characters."5