This definition of the tenth commandment has sobering ramifications. Covetousness, the unlawful desire to obtain, sets a person up for pursuing extreme acquisitiveness.
The actual mechanics of the process begin when the individual creates an idol in his mind in order to get something: a spouse, money, power, praise—even a feeling. None of these things are inherently evil, but in the process of achieving them, the person gradually allows the desire to have them to so dominate him that possessing them becomes his only worthwhile activity in life.
For a time, it actually shapes his existence. In desire's grip, he increasingly becomes consumed by it until he is committing other sins in order to achieve his aim. He will lie, steal, or ignore his spouse and children. The desire to get ultimately takes the place of God in many facets of his life, which affects the way that person responds to the true God.
Ephesians 5:5-7 declares this sin's seriousness:
For this you know, that no fornicator, unclean person, nor covetous man, who is an idolater, has any inheritance in the kingdom of Christ and God. Let no one deceive you with empty words, for because of these things the wrath of God comes upon the sons of disobedience. Therefore do not be partakers with them.
This is not a sin to fool with! The essential nature of this idolatry is selfishness, the worship of the self. A person's desire becomes the object of his affections and devotion.
A simple desire becomes coveting—a lust—when it drives us to sin in other areas of life. The sin may be actively or passively committed. Suppose we ask God for something He has promised, something good that He desires us to have—perhaps prosperity or healing. If our desire for that good thing becomes greater than our desire to submit to the way He says we must live in order to be prospered, it will motivate us to use carnal, sinful means to satisfy our lust. Did not Abraham do something similar in his desire to have a son?
This is the essence of the sin of covetousness and reveals why it is idolatry. God permits us to serve ourselves equal to the degree that we serve others. But if we serve ourselves at the expense of others—including God—and without regard for breaking God's other commandments, it raises mere desire to covetousness and then to idolatry. This idolatry is clearly serving the self.