Sun Tzu, the ancient author of The Art of War, believed the key to winning a battle was knowing both your enemy and yourself. “If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle.”

When it comes to our battle with sin, we must know our enemy and ourselves. Our enemy, Satan, is sinisterly active in our battle with sin (1 Peter 5:8). Satan tempts, deceives, lies, and devours.

But what about our relationship with sin? The lines between Satan’s actions and our own are, at times, closely linked in the Bible. Satan filled Ananias’s heart to lie to the Holy Spirit (Acts 5:3). Satan can tempt because of a lack of self-control (1 Corinthians 7:5). Satan can deceive us so that our thoughts are led astray (2 Corinthians 11:3).

How does this interplay between Satan’s temptations and our actions work? If we want to understand our enemy and ourselves, we must answer this question.

Itch Before Temptation

Perhaps our best guide for understanding how temptation and action work together is James 1:14: “Each person is tempted when he is lured and enticed by his own desire.” While the emphasis on ourselves instead of our enemy may surprise you, James teaches an important fact about how sin works by telling us that desire comes before temptation. It is not temptation by itself, but our heart’s desire for something that leads us into sin (James 4:1–2).

You can’t be tempted to do something you don’t desire. I can’t tempt you to eat a bowl of gravel. No matter how much I wave it tantalizingly in front of your face and woo you with sweet words of seduction about its texture and taste, you won’t find it tempting. Why? Because you have no desire to eat gravel.

We can only be seriously tempted by what we desire. Temptation, then, is not something that happens to us; it is something that happens within us. As James says, our own desires lure and entice us into sin. Our desires are our chief tempter. This should be a huge wake-up call for us. The way to fight sin is not mainly by trying to resist temptation. The most effective way to fight sin is by changing our desires.

Where Desires Come From

In order to change our desires, we must know where our desires come from. Desire can only exist where something is lacking. Desires are born out of a need, perceived or real, seeking to be met (Genesis 3:6). We desire food when our stomachs are empty. We desire warmth when our bodies are cold. Desires are born when we lack something.

Sinful desires, then, must come from a sense that we lack something. Why would someone abuse or oppress another person? Because they lack a sense of power or authority. Why would someone overwork at the expense of their family? Because they lack a sense of purpose or achievement. Why would someone cheat on their spouse? Because they lack a sense of fulfillment. Temptation is the offer sin makes to your desires to fill in the places that are empty.

But why do we choose sin over something else to fill in those places we lack? Why would we do what Isaiah 55:2 clearly advises against: “Why do you spend your money for that which is not bread, and your labor for that which does not satisfy?” The answer gets us to the root of all sin.

All Sin Comes from Unbelief

Unbelief is the root of every sin (Romans 14:23). We choose sin to fill the places in our lives that lack because we don’t believe God can really fill it himself. Jesus taught this principle in the Sermon on the Mount. He said that we get anxious because we don’t believe something about who God is for us. Jesus tells us that since God cares for the sparrows and flowers, he will care for us all the more (Matthew 6:25–34).

When we don’t believe this truth about God’s provision, we sin through anxiety. The chain reaction Jesus assumes in his teaching on anxiety can be traced as follows:

• Unbelief: We don’t believe in God’s provision (“O you of little faith”).
• Lack: We lack a sense of security and safety (“What shall we eat?”).
• Desire: We desire to feel protected and in control (“Gentiles seek after such things”).
• Temptation: Sin tempts us to figure out how we’ll fix it ourselves (“Do not be anxious”).
• Sin: We commit needless worry (“Which of you by being anxious can add a single hour to his span of life?”)

How to Fight Sin

So, how does knowing ourselves and knowing our enemy help us fight sin? If we want to fight a sin, we have to change a belief.

Consider the sin of anxious worry Jesus talked about. How do we stop being anxious? Well, it’s not just by saying no to its temptations. It is by changing what we believe about how God provides. Remember that since God cares for the “birds of the air” (Matthew 6:26) and the “lilies of the field” (Matthew 6:28), he will care for you who are “of more value” sparrows (Matthew 6:26). We don’t fight anxiety by trying to stop being anxious. We fight anxiety by “seek[ing] first the kingdom of God and his righteousness,” knowing that everything else we need “will be added” to us (Matthew 6:33).

The more we put our faith in the truth of who God is for us in Christ, the more he fills in the places within us that are lacking. As he does this, the Holy Spirit creates new desires within our hearts (Romans 8:1–11). These new desires cut temptation’s legs out from under it and lead us away from sin and toward holiness.