Covet means "to desire" or "to take delight in beyond God's acceptable bounds." It indicates "to long after a property that belongs to another in order to enjoy it." It is covetousness to allow oneself to indulge in thoughts that lead to actions named in the other nine commandments. They are grasping thoughts that lead to grasping deeds.
Coveting normally arises from two sources. It often begins with a perception of beauty in a thing desirable to possess. It also arises from a persistent inclination for something more abstract like a desire for power. The first is generally stimulated from without, the second generally from within. Both are equally bad.
One commentator stated that he believed all public crime would cease if just this one law were kept. Another said that every sin against one's neighbor, whether of word or deed, springs from the breaking of this commandment. James 1:14-15 seems to agree: "But each one is tempted when he is drawn away by his own desires and enticed. Then, when desire has conceived, it gives birth to sin; and sin, when it is full-grown, brings forth death."
In the Exodus 20:17 version of the commandment, the word "house" implies household. Subsequently, six other items are listed so that we clearly understand that "household" is meant. In Deuteronomy 5, "wife" is moved to first position as the very crown of one's possessions, and "field" is inserted because earlier, when God gave the Exodus version, fields were of no concern to pilgrims who possessed no land. Thus, between the two wordings God provides a seven-fold safeguard of other people's interests, revealing the underlying concept of outgoing concern.
In this commandment, we step from the outer world of word and deed into the secret place where all good and evil begins: the heart. The inner life actually determines a person's destiny, as the desires of a person's life are held and nurtured there.