Zero. The answer is zero. You can handle sin about as effectively as you can handle bullets in your vital organs—that is to say, not at all.

Sin destroys. Sin requires a life. Sin devours potential and crushes hope and separates you from God, which means there is no “safe” amount of sin. There is no “safe” amount of a thing whose only function is to rip your life to shreds.

Before the very first murder, what was God’s warning to Cain? “Sin lies at the door. And its desire is for you, but you should rule over it” (Genesis 4:7). Sin wants to own you. It wants to fill your heart and flood your life with its destructive effects. There’s a reason Paul warned against giving the devil a foothold (Ephesians 4:26)—even the tiniest crack in our armor is more than enough room for our adversary to work with.

With such a powerful enemy so eagerly focused on our destruction, we need a battle plan. Not too long ago, we talked about how removing sin from our lives requires a better plan than simply “not sinning.” The same principle is at work here: a solid defense against our enemy requires so much more than striving to “not give him a foothold.” That’s too vague; too abstract. We need a plan with action steps; with things to do, not just things to not do.

Solomon wrote, “Keep your heart with all diligence, for out of it spring the issues of life” (Proverbs 4:23). The issues of life begin with the heart. Who you are, your very identity, that begins with the heart. If our defense against Satan is to succeed, then it, too, must begin with the heart.

To “keep” our hearts means to protect them. To defend them. To guard them. The fact that such an action is necessary reminds us that something else—or rather, someone else—is looking for a way in. Jesus warned that “from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders, thefts, covetousness, wickedness, deceit, lewdness, an evil eye, blasphemy, pride, foolishness. All these evil things come from within and defile a man” (Mark 7:21-23). But where do all these actions start, do you think? Does a heart suddenly overflow with wickedness, or do these things begin as seeds, tiny thoughts and feelings that we allow into our hearts, nurturing and protecting them while they take root and begin to produce the fruit of wickedness? My money’s on the latter. I don’t think anyone wakes up evil one morning—I think that’s the result of a heart in which a lot of evil things were allowed to flourish.

Here, then, is the fundamental principle when it comes to not giving the devil a foothold: The things you let into your heart determine the things that come out of your heart.

Movies. Games. Music. Thoughts. Emotions. Friendships. Beliefs. These are the kinds of things that stand at the gate of your heart, demanding to be let in. Your job, every day, every moment, is deciding what gets in and what stays out. What meshes with God’s way of life and what doesn’t. When you’re in the movie theater and you realize the words or the images on screen don’t belong in your heart, there’s a decision to make. When you’re talking with a friend and you realize that relationship is taking you places you don’t want to go, there’s a decision to make. When the things you willingly let into your life don’t pass the Philippians 4:8 test—when they aren’t true or noble or just or pure or lovely or of good report or virtuous or praiseworthy—there are decisions to be made.

When we talked about spiritual vacuums, I had three steps for you. Today, I have only one. I’m sure we could put our heads together and come up with three, or seven, or a dozen, and I’m sure they’d each be good and valid and helpful. But I think this is the key step. I think this is the step that’s most necessary, most urgent, most uncomfortable to do, and most essential to our salvation:

Attack.

When the nameless Israelite waltzed into the camp with a Midianite woman on his arm, Phinehas grabbed his spear. Twenty-four thousand of his brethren had died in a plague because of their shameless idolatry and harlotry—twenty-four thousand, can you imagine?—so when this man marched into camp and advertised his clear intention to sin, Phinehas took action. With his spear, he walked up to the Israelite’s tent and skewered the two of them doing exactly what it sounds like they were doing (Numbers 25:1-9).

Be Phinehas.

Phinehas knew that the amount of sin the Israelite camp could handle was zero. They were the people of God. Twenty-four thousand corpses littered the camp because of an egregious sin, and here was a madman looking to reintroduce that exact sin while most of the camp was still weeping before the tabernacle. Unacceptable. Not even for a moment. Phinehas took up his spear and did something about it while the rest of Israel chose to stand by and watch.

When sin gathers at the gates of your heart, how do you handle it? Do you try to ignore it? Shoo it away? Let a little slip through the cracks as long as it’s not too much? Or do you follow the example of Phinehas, arm yourself for battle, and then eradicate it? Because that sin, however innocuous it appears, however innocent-looking, carries the seeds of destruction and death and you cannot handle it.

This is not a matter of building up a tolerance or developing an immunity. You can’t. It’s impossible. All sin—all shapes, all sizes—can and will destroy you if you give it a home in your heart.

In Deuteronomy, God inspired Moses to record one of the Bible’s most difficult passages. It’s not difficult because it’s hard to understand, but because it’s hard to accept. He told the fledgling nation of Israel,

If your brother, the son of your mother, your son or your daughter, the wife of your bosom, or your friend who is as your own soul, secretly entices you, saying, ‘Let us go and serve other gods,’ which you have not known, neither you nor your fathers, of the gods of the people which are all around you, near to you or far off from you, from one end of the earth to the other end of the earth, you shall not consent to him or listen to him, nor shall your eye pity him, nor shall you spare him or conceal him; but you shall surely kill him; your hand shall be first against him to put him to death, and afterward the hand of all the people. And you shall stone him with stones until he dies, because he sought to entice you away from the Lord your God, who brought you out of the land of Egypt, from the house of bondage. So all Israel shall hear and fear, and not again do such wickedness as this among you.

(Deuteronomy 13:6-11)

Your sibling. Your child. The spouse of your bosom, your friend who is as your own soul. Without question, these are the closest, most precious relationships any human being can have, and God singles them out to make a point. None of these relationships—not one, no matter how precious or how dear to our heart—none of these relationships are worth the price tag that comes with letting sin into our lives.

If this commandment seems harsh, consider Solomon, the wise king who warned us to guard our hearts. He failed to heed his own advice, and “it was so, when Solomon was old, that his wives turned his heart after other gods; and his heart was not loyal to the Lord his God, as was the heart of his father David. For Solomon went after Ashtoreth the goddess of the Sidonians, and after Milcom the abomination of the Ammonites. Solomon did evil in the sight of the Lord, and did not fully follow the Lord, as did his father David. Then Solomon built a high place for Chemosh the abomination of Moab, on the hill that is east of Jerusalem, and for Molech the abomination of the people of Ammon. And he did likewise for all his foreign wives, who burned incense and sacrificed to their gods” (1 Kings 11:4-8).

Ashtoreth, Milcom, Chemosh, Molech—these false gods were all pagan deities whose worship included everything from ritual prostitution to child sacrifice. I sincerely doubt that Solomon woke up one morning feeling like child sacrifice was a good idea. The road to that kind of depravity is a long one, littered with compromises and excuses and justifications—until one day the wisest man on earth is building furnaces for his people to burn their infants alive in the name of gods who don’t exist.

Solomon didn’t guard his heart. He tried to handle sin, and instead it handled him.

Israel was a people under a unique, nationwide covenant with God, so Deuteronomy 13:6-11 doesn’t translate perfectly into today’s world, but the principle remains: The closer and more intimate our relationship with someone, the more influence and sway that person holds over our hearts. When these people are pursuing a relationship with God, this is a fantastic principle. Iron sharpens iron and we all push ourselves to greater and greater heights. But when these people are pursuing other gods—modern gods of money or self-interest or pleasure—then this principle is dangerous. As the Bible says, “He who walks with wise men will be wise, but the companion of fools will be destroyed” (Proverbs 13:20). The people you let into your heart are the people with the power to change your heart.

Who are you letting in?

What are you letting in?

You cannot handle sin. Cannot. It lies at the door and waits, and it’s the only foothold Satan needs to step into your life and crush you.

Don’t give him the chance. Be Phinehas. Take your spear and annihilate whatever thoughts and actions threaten to stand between you and your God. Give no quarter, take no prisoners. A war is raging, and your heart is the target.

Will you keep it?