Here is question 3 in the 15-part Q&A with David Powlison on lusts of the flesh.
3. But what's wrong with wanting things that seem good?
What makes our desires wrong? The question becomes particularly perplexing to people when the object of their desires is a good thing. Notice some of the adjectives that get appended to our cravings: evil, polluted lusts (Col. 3:5; 2 Pet. 2:10). Sometimes the object of desire itself is evil: to kill someone, to steal, to control the cocaine trade on the Eastern seaboard. But often the object of desire is good, and the evil lies in the lordship of the desire. Our will replaces God's as that which determines how we live.
John Calvin put it this way: "We teach that all human desires are evil, and charge them with sin--not in that they are natural, but because they are inordinate" (Institutes, ed. Battles, p. 604). In other words, the evil in our desires often lies not in what we want but in the fact that we want it too much. Natural affections (for any good thing) become inordinate, ruling cravings. We are meant to be ruled by godly passions and desires (see Question 15). Natural desires for good things are meant to exist subordinate to our desire to please the Giver of gifts. Grasping that the evil lies in the ruling status of the desire, not the object, is frequently a turning point in self-understanding, in seeing the need for Christ's mercies, and in changing.
Consider this example. A woman commits adultery, and repents. She and her husband rebuild the marriage, patiently, painstakingly. Eight months later the man finds himself plagued with subtle suspiciousness and irritability. The wife senses it, and feels a bit like she lives under FBI surveillance. The husband is grieved by his suspiciousness because he has no objective reasons for it. "I've forgive her; we've rebuilt our marriage; we've never communicated better; why do I hold on to this mistrust?" It emerges that he is willing to forgive the past, but he attempts to control the future. His craving could be stated this way: "I want to guarantee that betrayal never, ever happens again."
The object of his desire is good; its ruling status poisons his ability to love. The lust to ensure her fidelity places him in the stance of continually evaluating and judging his wife, rather than loving her. What he wants cannot be guaranteed this side of heaven. He sees the point, sees his inordinate desire to ensure his marital future. But he bursts out, "What's wrong with wanting my wife to love me? What's wrong with wanting her to remain faithful to our marriage?" Here is where this truth is so sweet. There is nothing wrong with the object of desire; there is everything wrong when it rules his life. The process of restoring that marriage took a long step forward as he took this to heart.
Are preferences, wishes, desires, longings, hopes, and expectations always sinful then? Of course not. What theologians used to call "natural affections" are part of our humanity. They are part of what makes humans different from stones, able to tell the difference between blessing and curse, pleasure and pain. It is right that we don't want the pains of rejection, death, poverty, and illness, and we do want the joys of friendship, life, money, and health. Jesus was no masochist; of course he cried out, "Let this cup pass from me!"
The moral issue always turns on whether this desire takes on a ruling status. If it does, it will produce visible sins: anger, grumbling, immorality, despair, what James so vividly termed "disorder and every evil thing" (James 3:16).
Jesus was no idolater; he entrusted himself to his Father and obeyed. "Nevertheless, not my will but yours be done." If natural affections remain submitted to God, such faith will produce visible love. If you wish your son to grow up to be a Christian, and he strays, it may break your heart, but it will not make your sin against either God or your son.