Fight Sin

“Be killing sin, or it will be killing you.” John Owen
“For if you live according to the flesh you will die, but if by the Spirit you put to death the deeds of the body you will live.” Romans 8:13
We must not take a passive posture in relation to our sin. Scripture exhorts us to “Put off your old self which belongs to your former manner of life and is corrupt through deceitful desires, and to be renewed in the spirit of your minds” (Eph. 4:22-23).

Since we have been united with Christ by faith, we are free from the penalty of sin (Rom. 8:1) and from its controlling power (Rom. 8:2). “Sin is still your enemy, but it is no longer your master” (Colin Smith). We are free in Christ, but we are not free to continue in sin or to presume upon the grace of God. No! We are free to walk in the new life of the Spirit; free to love God with all of our hearts; free to pursue holiness and increasingly reflect the image of Christ our Lord. 
The key to battling sin and temptation is to replace our old desires and loves with new and better ones in the Lord. While we must be proactive in our fight with sin, we must not become preoccupied with a focus on sin. Rather, we need to stoke the flames of worship in our hearts and constantly direct our thoughts to the glory and majesty of our God. And as we see His greatness and experience His goodness, “the things of earth will grow strangely dim in the light of His glory and grace.” 
“For every look at sin, take ten looks at Jesus.” Robert Murray-M’Cheyne
The secret to a life of holiness is a heart of godliness. To be godly is to give God weight in your life – to make Him central and exalt Him as Lord. A godly person thinks much of God and little of himself. A godly person considers God’s will in all things and constantly surrenders her own desires. “He must become greater, I must become less.”
So the first battle in the war against sin is making a firm commitment to worship – both corporately and personally. We have become very influenced by our culture of rampant self-indulgence and this has resulted in a dramatic reduction in the importance of Sunday worship. Nearly every whim of ours can be an excuse to skip church – the slightest cold, plans that ran late Saturday night, the need to catch up on work, a desire to extend a weekend getaway, a little trouble getting the kids ready… the list goes on. We must reclaim the sanctity and priority of Sunday as the Lord’s Day and re-elevate the importance of gathering as God’s people to worship Him together. Our daily lighting of a candle unites each Sunday in the bonfire of public worship.
Similarly, in our great concern to prevent legalism, we have nearly lost sight of the importance of spiritual disciplines. Many of us give lip service to the need for daily prayer and Bible reading but the reality is that we place almost every other task ahead of these in terms of priority so that our “quiet time” becomes a “if I get around to it” reality. 
“I ought to pray before seeing any one. Often when I sleep long, or meet with others early, it is eleven or twelve o’clock before I begin secret prayer. This is a wretched system. It is unscriptural. Christ arose before day and went into a solitary place. David says: ‘Early will I seek thee’; ‘Thou shalt early hear my voice.’ Family prayer loses much of its power and sweetness, and I can do no good to those who come to seek from me. The conscience feels guilty, the soul unfed, the lamp not trimmed. Then when in secret prayer the soul is often out of tune, I feel it is far better to begin with God—to see his face first, to get my soul near him before it is near another.” Robert Murray M’Cheyne
We need discipline, but within that discipline there must be devotion:
“You read your Bible regularly, of course; but do try and understand it, and still more, to feel it. Read more parts than one at a time. For example, if you are reading Genesis, read a psalm also; or, if you are reading Matthew, read a small bit of an epistle also. Turn the Bible into prayer. Thus, if you were reading the 1st Psalm, spread the Bible on the chair before you, and kneel, and pray, ‘O Lord, give me the blessedness of the man,’ etc. ‘Let me not stand in the counsel of the ungodly,’ etc. This is the best way of knowing the meaning of the Bible, and of learning to pray.” Robert Murray M’Cheyne
Finally, the other side of the battle with sin is to actively confront and attack the remaining sin in your life. “Know your sin. Stalk your sin. Kill your sin” (Colin Smith)
“We need to be intimately acquainted with the ways, wiles, methods, advantages, and occasions which give sin (lust) its success. This is how men deal with their enemies. They search out their plans, ponder their goals, and consider how, and by what means they have prevailed over them in the past.  Then they can be defeated… We need to… trace this serpent in all of its turning and windings, and to bring its most secret tricks out into the open.  We must learn to say – ‘this is your usual method; I know what you are up too.’” John Owen
“[Sin] will not die except by being gradually and constantly weakened: Spare it and it heals its wounds, and recover its strength. Everything will do its utmost to preserve its life and being. So will sin do also; and if it be not constantly pursued with diligence and holy violence, it will escape our assaults. Let no man think to kill sin with a few easy or gentle strokes.  He who has once smitten a serpent, if he follow not on his blow until he be slain, may repent that ever he began the quarrel.  And so he who undertakes to deal with sin, and pursues it not constantly to death.” John Owen
“The first thing in mortification is the weakening of this habit. This is called ‘crucifying the flesh and the lusts thereof (Gal 5:24); that is, taking away its blood and spirits that give it strength and power.
As a man nailed to the a cross he first struggles and strives and cries out with great strength and might, but, as his blood and spirits waste, his strivings are faint and seldom, his cries low and hoarse, scarce to be heard;  when a man first sets on a lust or distemper, to deal with it, it struggles with great violence to break loose; it cries with earnestness and impatience to be satisfied and relieved; but when by mortification the blood and spirits of it are let out, it moves seldom and faintly, cries sparingly and is scarce heard in the heart. Sin …is fastened to the cross… that… the power of sin [be] weakened and abolished by little and little.” John Owen

Every time you say “yes” to a sin you increase its power in your life. Every time you say “no” to a sin you decrease its power in you. We will not reach perfection in this life, but perfection must still be our aim lest we compromise with the deceitfulness of sin. We will not become perfect, but we will make progress. We will grow. We will gain victories in the mortification of sin for the Spirit of Jesus Christ dwells in us and His power is at work in us to “bear the fruit of righteousness that comes through Jesus Christ, to the glory and praise of God” (Php. 1:11).