It’s fair to say there’s too much war in the world, and yet there’s a war you ought to be involved in everyday – the war on sin.
Sin is your enemy. It will kill you. In your war on sin you need to be ready to put sin to death, without pity or sentiment.
At our Bible Overview a week or two ago we were thinking about the relationship between the Old Testament and the New. As you look at something like Deuteronomy 20 with its rules about war you might think it’s no longer relevant. But we were thinking about how many Old Testament laws are both ‘of the time’ for the nation of Israel, and also reflect something of God’s morality.
So the principles underlying war in Deuteronomy 20 are also helpful to you in your war on sin today.
These notes accompany a sermon on YouTube delivered at Bromborough Evangelical Church on 6th April 2025. You can find more in the series in our sermon index.
So first:
Know what you’re fighting for (1-7)
The Israelites were being sent into Canaan, the Promised Land, knowing it was already occupied. The people already there worshipped other gods, and carried out awful practices in the worship of those gods. So when God sent Israel into Canaan they would be removing the pollution of sin – and bringing judgment to those nations.
But that’s obviously pretty scary. So read Deut 20:1.
They were being told to step forward to take hold of everything that God had promised them. It would be hard work, rooted in God’s promises. But they would succeed because God was with them.
That’s the weight and promise of verses 1-4. A priest would address the army in the place of God himself. But then something odd would happen.
Knowing that your army is weaker than your enemy’s army, you’d probably not want to weaken yourself further! But they did: Read Deut 20:5-7.
It’s not an obvious military strategy, to weaken your army. Obviously, having the Lord on your side means you’re never actually weakened – especially when the enemy is ungodly and sinful.
But why send those men home? The simple reason is that everyone engaged in the battle must know what they’re fighting for, what they’re protecting.
Now, you’re not in a battle like that. But you are in a battle.
Spiritual warfare
Read Ephesians 6:11-12: Put on the full armour of God so that you can stand against the schemes of the devil. For our struggle is not against flesh and blood, but against the rulers, against the authorities, against the cosmic powers of this darkness, against evil, spiritual forces in the heavens.
Your battle is against the schemes of the devil worked through unseen evil in the world. What schemes? He’ll tempt you to sin – to discredit the gospel, the church, and Christ himself. He especially aims at church leaders. And he’ll work towards division in the church – through gossip, chitchat, grumbling. Weigh your words: Are you a grumbler? By all means raise things that need fixing, but don’t grumble away in a corner.
And if you have never yourself come to faith then the devil already has you where he wants you. He’s a liar. He’ll fill your head with questions and doubts and reasons why you can’t become a Christian. But God is truth. God is grace. He stands always ready to forgive and to love. You turn to him, and let the devil be damned.
Paul goes on in Ephesians to tell you to put on the whole armour of God – armour God gives you to fight your daily spiritual war. Have “your feet sandaled with readiness for the gospel of peace.” Readiness! Don’t wait for trouble, but take steps every day to be ready to fight against sin, temptation and injustice.
What are you fighting for?
But know what you’re fighting for.
- Fight for purity of heart – knowing that a clear conscience is so much better than a burden of guilt and sorrow. The more you know that, the more you’ll want to fight for it.
- Fight for kindness in speech – seeing the thrill of others growing, being encouraged, built up. The more you see that, the more you’ll want to be that kind person.
- And fight for unity among believers – knowing the damage that disunity brings. Work to ignore gossip, and to encourage forgiveness in your own heart and others too.
Fight to know Christ better, knowing by experience that to live is Christ. He came that you would have life to the full. So work and fight to experience more and more of him.
As you know what you’re fighting for, you’ll be ready to fight again. So:
Be focussed on Christ (8-9)
The army in Deuteronomy 20 was almost ready. But there was another group of men to be sifted out before they could go forward: Read Deut 20:8-9.
Now you can most certainly be brave and scared at the same time. If anything, if there’s no fear then there’s probably no bravery, because bravery is action in the face of fear and danger.
But that’s not the same as being afraid and cowardly: Such men weren’t fit to fight simply because their heart wouldn’t be in it. In combat, you need men ready to step forward despite fear.
So by verse 9, the army is ready.
Everyone there is focussed ahead, ready to serve, to fight.
Focussed ahead
Jesus calls his people to the same single-minded focus of pressing ahead. For Jesus, in Luke’s gospel, there’s a key moment where we’re gold that he “set his face” for Jerusalem, for the cross. He was fixed on the task ahead and wouldn’t be swayed from it. Likewise, you’re to have your eyes fixed on Christ, knowing that you will have to take up your cross on the way.
Some people told him boldly that they’d follow him anywhere.
Luke 9:61-62: Another said, “I will follow you, Lord, but first let me go and say good-bye to those at my house.” But Jesus said to him, “No one who puts his hand to the plough and looks back is fit for the kingdom of God.”
If you’re ploughing your field with your ox and you keep looking over your shoulder, your ploughing will soon be off course.
Look ahead: Look to Christ. Set your affections on him. Flee from every form of idolatry. Lay everything you have and are at his feet and follow him. Meditate on him. Know him.
Spend time with him. Real time, not just snatches. Enjoy Jesus.
Role models
Hebrews 11 is a long list of Old Testament people who went through all sorts of troubles and difficulties, but with one thing in common: “All these were approved through their faith, but they did not receive what was promised” (Hebrews 11:39). They were looking ahead, living by faith all their lives.
Hebrews goes on to say that Christ himself acted in the same way: “For the joy that lay before him, he endured the cross, despising the shame, and sat down at the right hand of the throne of God.”
So with a cloud of witnesses and Christ himself so focussed on what was ahead, what should you be like?
Hebrew 12:1-2: Therefore, since we also have such a large cloud of witnesses surrounding us, let us lay aside every hindrance and the sin that so easily ensnares us. Let us run with endurance the race that lies before us, keeping our eyes on Jesus, the pioneer and perfecter of our faith.
Is that your experience? Do you really think your life is directed and focussed on Jesus?
- What hinders you?
- What sins ensnare and entangle you?
- What distracts you from him?
- He is your Lord and Saviour, and to know him is life itself. If you prefer other distractions, repent!
Jesus is Lord, and he is God With Us.
You have Christ in you, the hope of glory.
You are in union with the eternal Son of God, indwelt by the Holy Spirit of Adoption, and the Father holds you in his heart.
Let nothing hinder you
Will you let sin, temptation, or indulgence keep you from him? Is it your job? Laziness? Idols or excuses? Repent!
And be careful: Don’t use church or religion as a substitute for the real thing. You must yourself go and spend time with Jesus. There’s nothing better you can do with your time anyway. Repent.
Jesus is life now. He’s the way and the end of the journey. He has life in himself, and he gives it freely to all who ask.
So enjoy your union with him. Experience more of him, focus on him, strive towards him. He is the very communication and representation of the Father to you; if you are to enjoy God, you are to enjoy him in Christ.
And if you’re to do that, then there’s an enemy to slay. You are in a war on sin:
Put sin to death (10-18)
When Israel went to fight against a city, there were different rules depending on whether the city was inside the Promised Land of Canaan or outside it.
Deut 20:10-15 deals with cities outside Canaan. They were to begin with an offer of peace. If peace was acceptable, they’d subdue the city and spare it. But otherwise, they’d lay siege and then kill all the men.
But there was to be no offer of peace within Canaan: Read Deut 20:16-18.
This was an act of judgment from God for their idolatry and wicked practice. And it was protection from idolatry for Israel: They would only be blessed under God’s covenant if they remained true to God. Ironically, the practice was for blessing.
Now this distinction of war on sin ‘outside’ and ‘inside’ is helpful as we think about the war on sin that we’re engaged in.
There’s no place for sin in you or in the church, but you’re obviously limited in what you can do beyond that.
Put sin to death in yourself
Examine your own heart:
- Do you put up with sin in your heart, finding excuses? Even allowing something to stay and presuming on God’s grace?
- Christ’s sermon on the Mount makes it clear that you sin in your heart before you sin with your hands: Your desire to sin shows how sinful you still are.
- Or maybe you don’t sin largely because you fear the consequence – you’d sin if you could get away with it?
It’s all so shabby, compared with the glory of Christ.
Look to Jesus. Raise your vision. John Owen put it this way: When he shall bring us into his presence we shall cry out, “We never knew him as he is; the thousandth part of his glory, and perfection, and blessedness, never entered into our hearts.” …We who cannot behold the sun in its glory are too weak to bear the beams of infinite brightness. (p169, mortification of sin)
And it’s that Christ who died for you! His death for your sins.
Put sin to death by the Spirit of God in you, not least by raising your eyes to Jesus.
Put sin to death in the church
In 1 Corinthians 5, Paul speaks of expelling a Christian from the church who is living in open rebellion and sin.
- Where Deuteronomy had different laws for those inside and outside Canaan, it’s the same for those inside and outside the church.
- An unbeliever is welcomed as an unbeliever; but a believer living as an unbeliever is to be expelled: It’s the sin among us that’s being removed. Restoration is always the aim.
- That does mean separation from churches that call evil good and good evil, who bless sin as if it’s good.
Put sin to death in anticipation
Imagine the sheer pleasure of existing without sin, regret, hurt, a bruised conscience, or the need for apology. A life in perfect, blissful communion with the living God, delighting him and delighting in him every day. As a Christian, that’s your destiny: As sinless as Christ himself.
Whet your appetite: Put sin to death, and live for Jesus now.
Summary
- Deuteronomy 20 has rules for war. You are in a spiritual battle. The enemy within is sin; the enemy outside is Satan. You’re to fight.
- Know what you’re fighting for. The more of Christ you experience the more you will want to fight against the dark forces that would harm you.
- Be focussed on Christ: Don’t put your hand to the plough and look over your shoulder: Go to him; fix your eyes on him. Don’t be encumbered by sin or idolatry.
- So put sin to death: In you, in the church, and in anticipation of all that’s to come. Don’t make excuses. Raise your eyes to Christ in all his glory, and put one foot in heaven in a life of godliness, enjoying Jesus every day.