A while back, someone asked me about covetousness. What’s below is what I wrote in reply, slightly edited for posting here.
Desire is a good thing. There is such a thing as the “desires of the Spirit” which ought to be pursued in contrast to “desires of the flesh” (Galatians 5:17—granted the Greek word “desire” here is only directly attached to the flesh clause, but there is still an implied contrast between the “desires” of each).1
One of the “desires of the flesh” that Paul lists is “envy” (Galatians 5:21), which is close to covetousness—not named in this passage explicitly but certainly one of the “things like these.” The difference between envy and covetousness being, probably, that “envy” carries a nuance of bitterness against the blessings or prosperity that others have, where covetousness is more of a discontent toward not having those things yourself. Covetousness means you have strong desire for what is not yours, where envy means you want the one who has it to go without. Envy implies bad feelings toward others. Covetousness implies—more simply—discontent with God’s providence. There is overlap and the two can easily bleed into each other, but covetousness seems to be in a way more self-centered. The concern is not so much with what others have (as with envy), but with what you lack.
And covetousness is not simply desire for what you don’t have, as if there is no proper place for ambition or desire for growth. Again, desire itself is a good thing. It isn’t even wrong to desire things that you lack. Wanting good things and pursuing them in lawful ways is good. We wouldn’t grow otherwise. Where covetousness is sin, I think, is in wanting something 1) Inordinately (this would be basically equivalent to greed), or 2) Wanting something that is not lawful to have (this would be what the 10th commandment specifies - coveting your neighbor’s house, wife, animal, etc).
What is it to want something “inordinately”? That can require discernment. But some helpful questions to assess this might be: Is it a desire that dominates? Does it it keep you from joy? Does it keep you from peace? Are you willing to sin in other ways to achieve it? Does it dampen your ability to “rejoice with those who rejoice”? Is it so strong that it means you are not “seeking first the kingdom of God and his righteousness”? Perhaps also, why do you want the things that you want?
The other side of covetousness, wanting something that is not lawfully yours or is clearly providentially denied to you, is perhaps why Paul equates covetousness with idolatry in Colossians 3:5, “Put to death therefore what is earthly in you: sexual immorality, impurity, passion, evil desire, and covetousness, which is idolatry.” Covetousness in this sense means discontentment with God’s providential ordering of your circumstances, and implies rejection of God himself. Perhaps the basic biblical illustration of this is Israel’s continual complaining in the wilderness - lack of food and water, lack of the kind of food that they wanted, discontent with Moses as their leader, and so on. They wanted to go back to Egypt, and by implication wanted to return to Egypt’s gods. Their coveting what God was denying to them was therefore ultimately a form of idolatry. Their “lust for flesh” in Numbers 11:4 soon blossomed into seeking a new leader to take them back to Egypt (Numbers 14:4) and God’s accusation that they had despised him and abandoned faith in him (Numbers 14:11).
Now, food and water are good things, even necessities. It wasn’t wrong to want them, and wouldn’t have been wrong to seek them (wouldn’t they have to regularly be on the lookout for sources of water?)—The sin was the grumbling, the murmuring, the rebellious attitude, the unbelief in God’s goodness and wisdom, and the desire for a different provider and sustainer—and in Numbers 11 at least, the “strong craving” that was beyond reason.
As our Lord said, “Take care, and be on your guard against all covetousness, for one’s life does not consist in the abundance of his possessions” (Luke 12:15).
Galatians 5:17 “ἡ γὰρ σὰρξ ἐπιθυμεῖ κατὰ τοῦ πνεύματος, τὸ δὲ πνεῦμα κατὰ τῆς σαρκός, ταῦτα γὰρ ἀλλήλοις ἀντίκειται, ἵνα μὴ ἃ ἐὰν θέλητε ταῦτα ποιῆτε.”