"You shall not covet" (Exodus 20:17 and Deuteronomy 5:21). The last of the Ten Commandments—against coveting—is aimed directly at the heart and mind of every human being. In prohibiting coveting, it defines not so much what we must do but how we should think. It asks us to look deep within ourselves to see what we are on the inside. Covet means to crave or desire, especially in excessive or improper ways. The Tenth Commandment does not tell us that all of our desires are immoral. It tells us that some desires are wrong.
Coveting is an immoral longing for something that is not rightfully ours. That is usually because the object of our desire already belongs to someone else. But coveting can also include our wanting far more than we would legitimately deserve or that would be our rightful share. The focus of the Tenth Commandment is that we are not to illicitly desire anything that already belongs to others.