In John Owen’s well-known work on sin and temptation, he defines two kinds of temptation: ones that come from without and others that come from within (Works, 6:194). The first kind of temptation works like this. I am hungry. And someone offers me stolen food. This temptation comes from without and is morally neutral.
The second kind of temptation works like this. From within me, I propose a desire to steal food for the pleasure of eating. According to Owen, “the very proposal from within, it being the soul’s own act, is its sin” (Works, 6:194).
Although this taxonomy of temptation may seem overly detailed, it becomes important when we ask the question: when does temptation become sinful? Or more specifically, when does sexual or romantic desire become sinful?
Married and tempted
Here is what I mean. A married woman rightly can desire her spouse romantically and sexually. But what if she recognizes another man as an attractive man? Since polygamy is unnatural, does this recognition of beauty constitute sin? Has she experienced “evil desire” (Col 3:5)?
I answer no. In Matthew 5:28, Jesus defines when desire for someone becomes sin. He explains, “When someone looks at a woman for the purpose of lusting after her (pros to epithumesai auten), he has already committed adultery in his heart.”
Note two items. First, seeing a woman and recognizing the aesthetic appeal of that woman is itself not wrong. Jesus specifies that looking with lustful intent is wrong. The Greek construction pros to epithumesai auten signifies purposeful intent.
Second, the sinful act occurs “in his heart.” A desire that arises in our heart arises from within our fallen nature. This desire itself is sinful, or in the language of Paul is an “evil desire” (Col 3:5).
While Jesus gives a general principle, we can apply it to a married person. If the woman in the above example, sees a man whom she considers attractive, she does so without sin—if she does not look with lustful intent.
While polygamy or adultery are unnatural desires, she does not desire either by recognizing the aesthetic appeal of a man. However, if she looked with lustful intent, then she would desire something that is against nature—either adultery or polygamy if she desires more than one spouse.
Single and tempted
What about a single person who desires marriage. Does lust, in this scenario, constitute sin? Again, Jesus himself says that looking at someone with lustful intent is adultery (unnatural sex since it occurs outside of marriage).
What about sexual desire while dating or engaged? The desire for sexual experience should not be the basis for non-married attraction. What should attract us to someone? Certainly, physical beauty plays a role. But so does character. Virtue and beauty work together to make someone attractive. Not the desire for sexual experience.
That my statement may seem impossible may reveal how incredibly oversexualized our culture has become. If attraction means sex, we have a problem.
But it is not as if sex itself is ignored in Christian thought. When someone has entered into an agreement to marry (engagement), both people know that sex will come. During this time desiring sexual union becomes not only acceptable but virtuous.
Two people desire the main sign of marital unity whose purpose lies in the very mystery of the incarnation, namely, the marriage of Christ and the church. Reading the Song of Songs illustrates how this can look in practice.
Temptation becomes an evil desire (e.g., adultery in the heart) when we look at a person for the purpose of lusting. Recognizing the aesthetic beauty of a person is not an evil desire—even if that person is not a spouse. Yet the moment that this recognition births evil desire in the heart by looking with lustful intent, it is sin.
While this article only goes so far, we also need to realize that even married desires for each other can be sinful. We can wrongly desire each other by doing harm physically and emotionally to each other and through a host of other means.
So Jesus’ teaching on internal desire has practical implications for any sort of relationship. I focused on the above two examples because they represent two simple ways to illustrate how temptation becomes sin.