This particular question is at least as old as the New Testament. The question is formatted in a slightly wrong way. The question is not why live a life of faithfulness “if” we are already justified/counted righteous in Christ but rather “since” we are counted righteous on the basis of someone else’s righteousness (Jesus) then why live a life of good deeds. The fact that our right standing with God is dependent entirely on faith in the finished work of Christ and not owing to anything in ourselves in concrete faith. That is the gospel. Christ has done what we had to and has taken the penalty for our failure to do so. We are partakers in this great salvation, not by cooperation, but by turning from our attempts to justify ourselves and thrusting ourselves completely on Christ. This is what Paul is getting at in Romans 5 when he says, “as one trespass led to condemnation for all men, so one act of righteousness leads to justification and life for all men. For as by the one man’s disobedience the many were made sinners, so by the one man’s obedience the many will be made righteous.” You and I cannot do anything to commend ourselves to God. Even our greatest works are pure sin if they do not come from a justified heart, liberated to be obedient by the obedience of another. Sin abounded, but grace abounded all the more.

Now this has led some to ask, “Since God has saved us completely by grace, why should we do good?” Paul anticipates this question at the beginning of Romans 6. He writes: “What shall we say then? Are we to continue in sin that grace may abound? ” To some, the logic of justification by faith leads to living however one wants. God’s grace covers us and therefore who cares how we live. God will give grace. Paul’s answer to this question was “by no means.” But why? Many have given different answers to this question. The 18th century evangelist John Wesley posited that salvation cannot be completely based on the righteousness of Christ because that would promote lawlessness. Where is the motivation, Wesley wondered? If God has done it all in Christ, why should we strive and fight to live righteous lives? And this led Wesley to compromise a key part of the gospel.

But Paul saw no contradiction between justification by faith and fighting to live moral lives as believers. For Paul, this justification that is by faith alone in Christ alone is fuel for the fight of faith; not the water that would quell the flame. Charles Spurgeon certainly saw this as the case saying,

You will not find on this side heaven a holier people than those who receive into their hearts the doctrine of Christ’s righteousness.

So why fight for holiness whenever we have been completely justified by the holiness of another?

The Holiness of God in the Gospel

First, the one who sees the insufficiency of anything in himself to save him is one who has seen the holiness of God. God being holy means He is perfect, set apart. God does not require we do our best. His goodness requires goodness. Perfect goodness. That is what makes the call for us to love God with all of our heart, mind, soul and strength such bad news to sinners. Jesus there in Luke is pointing to our insufficiency, not to our sufficiency. We Jesus says all then he means just that. The Ten Commandments found in Exodus are a reflection of the character of God. One cannot be justified by just doing good enough. Getting 7/10 is not a passing grade. A 10/10 is required and that is impossible because we are sinful to the core. One errant thought is worthy of eternal damnation. God is good. God is gloriously worth. And He will not be mocked.

Isaiah saw his sin in the light of God’s holiness in Isaiah 6. Hear the Word of the Lord through him:

In the year that King Uzziah died I saw the Lord sitting upon a throne, high and lifted up; and the train of his robe filled the temple. Above him stood the seraphim. Each had six wings: with two he covered his face, and with two he covered his feet, and with two he flew. And one called to another and said: “Holy, holy, holy is the LORD of hosts; the whole earth is full of his glory!” And the foundations of the thresholds shook at the voice of him who called, and the house was filled with smoke. And I said: “Woe is me! For I am lost; for I am a man of unclean lips, and I dwell in the midst of a people of unclean lips; for my eyes have seen the King, the LORD of hosts!” Then one of the seraphim flew to me, having in his hand a burning coal that he had taken with tongs from the altar. And he touched my mouth and said: “Behold, this has touched your lips; your guilt is taken away, and your sin atoned for.” (Isaiah 6:1-7 ESV)

Isaiah, more than likely, was quite moral. But in the presence of absolute goodness, he trembles. The standard is not one you set for yourself or your neighbor. No, those are far too attainable. The standard is God. And God is majestic. The goodness and majesty of God is our worst nightmare outside of Christ. That is because we have attempted to gain this glory ourselves, fancying ourselves majestic and worthy of praise. But in the light of true beauty we see how ugly we really are. Isaiah renounces himself saying, “Woe is me!” He is undone in light of God’s holiness. It is precisely at this point God atones for his sin. Only the sufficient sacrifice of God can save Isaiah from sin. A burning sacrifice from the mercy seat of God is applied monergistically to his lips, just as the work of Christ is applied to us by the Holy Spirit.

Therefore, having received the free grace of God, what does he do? He does not go on living the same way. He is sent out in obedience. Free from trying to justify himself, Isaiah goes to fulfill a particularly hard ministry. It is the explosive power of the holiness of God that produces obedience. It seems those who esteem themselves least and esteem God most are those who live in radical obedience to Christ.

We get this sense in Romans 1 as well. The gospel is called the “power of God unto salvation” by Paul in verse 16. Why is that? “For” it contains the righteousness of God. The righteousness of God can be defined much like the holiness of God. It refers to the intrinsic goodness and justice of God. But here, the righteousness of God has two meanings. It is indeed referring to the righteousness of God. We have already noted that in the Christian gospel we see a holy God. But Paul is also referring to a righteousness from God, a gifted righteousness to be had by faith. This is precisely how a righteous God and unrighteous people coexist in communion forever. Those who see their need for the righteousness from God are those who have seen the righteousness of God most fully. That is transformative. When we see the ugliness of our sin in light of God’s worth, we will have no other option than to fight to kill sin and enjoy the holiness of God. We become what we behold.

Gospel Motivation

Let’s see what Paul said to answer the hypothetical question, “Should we sin that grace should abound?” He asks back, “How can we who have died to sin still live in it?” Basically, he is speaking to the believer’s new position and identity in Christ. The theme of Romans 6 could be summarized by saying the believer is alive to God and dead to sin. Before Christ, we are very much alive to sin. We presented our members fully to sin to do its bidding. But in Christ, we have fundamentally change. We have been brought to life, enabled to see the glory of Christ. Christ’s sweetness makes sin bitter. Being alive to God necessarily entails being dead to sin. Since we have been brought to life, justified in Christ we now present ourselves to God as such. We fight to use all of our members as instruments for righteousness. We are enabled to do this because we have been crucified with Christ.

Paul tells us in Romans 8 that “there is therefore now no condemnation for those who are in Christ Jesus.” This is one of the most beautiful declarations of God’s free justification in all of the Bible. We sinners, who are in the midst of Romans 7 currently, are simultaneously declared to be just before the God of holiness. There is no condemnation is left; Christ has taken it all. We are as just as Jesus is. We have as good a chance of being judged for our sin as Jesus does. If we fell from justification it would mean that Jesus has. And He will not. We are now in the Spirit and not in the flesh. Our minds, then, our set on the things of the Spirit. So now in Romans 8:13 we are encouraged to put to death the deeds of the flesh by the Spirit. We are not left to mortify the flesh by our willpower. The Spirit, applying the work of Christ, powers our obedience. If we do not kill the flesh, we will die. But since we are in Christ we will necessarily kill sin.

The entire book of Hebrews is about the atonement of Christ. Jesus is the great end for which the sacrificial system aimed. He is the Great High Priest. He is the sacrificial Lamb. His sacrifice has effectively reconciled us to God, based on nothing but His person and work. Two passages in Hebrews in particular show us the relationship between what Jesus has accomplished on our behalf and how that effects our sanctification. The tenth chapter of Hebrews focuses on Jesus as the perfect sacrifice for sin. The priests of the OT had to repeat the sacrifices over and over again. They were insufficient, because they point us to something greater: Jesus. Jesus was the perfect atonement, taking the entirely of God’s holy wrath on Himself; exhausting the justice towards our sin that we deserved. The passage comes to a head in verse 14. It reads: 

For by a single offering he has perfected for all time those who are being sanctified. (Hebrews 10:14 ESV)

This perfect sacrifice is finished. And yet sanctification is progressive. Justification (declaration) grounds sanctification (ongoing). The root of our sanctification is the perfect atonement of Christ. We are already perfected, but are currently being perfected experientially. The basis of our confidence before God is the finished work of Christ. But that sacrifice is used by God to animate us, causing us to walk in obedience.

Hebrews 13 is one of the clearest texts when considering these things. John Piper formulates sanctification like this, “God works the miracle and we act the miracle.” Lest we make a grave error we must reckon that sanctification is all of grace too. This grace is one that animates instead of declares and yet they stem from union with Christ by faith.  Hebrews 13:20-21 reads: “Now may the God of peace who brought again from the dead our Lord Jesus, the great shepherd of the sheep, by the blood of the eternal covenant, equip you with everything good that you may do his will, working in us that which is pleasing in his sight, through Jesus Christ, to whom be glory forever and ever. Amen.” Catch that? God is working in what is good and pleasing in His sight. To be sure, we are to walk in them (Eph 2:10). But it is the free grace of God, flowing to us from the cross of Christ, that works a miracle in our hearts to long for holiness. We must get this. The fight for holiness is hard but not one undertaken by gritting your teeth and begrudgingly following Christ. God enables us to see that holiness is for our greatest happiness. We must walk in holiness. But that holiness is enabled only because of the gospel. It is the great shepherd of the sheep and his “blood of the eternal covenant” that enables us to walk in imperfect obedience. We can walk in a manner pleasing to Christ. Indeed we must. But we do so, not to be justified, but because we have already been declared as such.

Gospel Warning

There is an appropriate place for warning in our pursuit of holiness. It is, again, the sheer grace of God that these warnings cause us to be watchful over our hearts. Because friend, our justification will be evidenced by sanctification. If there is no pursuit of holiness in your life, then you have little reason to be assured of your salvation. Please, please hear me. You are not saved by this fruit. Even our best deeds could not move God towards us. They are imperfect fruits, but they are real. You are not being pious by living in sin but saying that all salvation is all of grace. It is! O how freely God gives grace. But this grace causes you to die to yourself. It gives you a heart sensitive to sin. J.C. Ryle once said that the Christian is known for two things: his inner peace and his inner warfare. If you are fighting sin but it keeps rearing its ugly head, take heart. Even as you grow in holiness, you will see how insufficient it is. But you must grow in holiness.

Jesus gave the illustration of trees and fruit. A good tree bears good fruit (Matthew 7). These fruits are listed in Galatians. A bad tree cannot bear good fruit but instead produces the works of the flesh, found also in Galatians. Friend, you cannot make yourself a good tree. Only the gospel makes you a good tree. Christ is the tree vine and apart from His finished work we can do nothing. But if you are truly made a good tree, you must bear good fruit. A confession of faith means nothing if it is not accompanied by a changed life. Sanctification is slow and hard. At times, we cannot even tell if we are growing. We must look to Christ as our assurance. Ask good brothers and sisters if they see genuine gospel fruit in your life.

You Become What You Behold

The main motivation to fight for holiness is to see God. In conversion, our eyes are opened to the supreme value of Christ. He is like a pearl of great price, a supreme treasure (Matthew 13). Jesus becomes our all in all. To know Him more, we must fight. The fight of faith is a fight to see. Indeed, Paul says that we are transformed from one degree of glory to the next, not by straining in our own power and being really good, but by beholding the glory of Christ. The more we see Him in His splendor, the holier our lives will be. We want God and we will fight tooth and nail to see Him. This requires painstaking effort. But the effort is driven by the fact the we are not working up to God, trying to attain Him. No, we have received full adoption as sons of God because of Jesus dying in our place. Knowing this, we are free to fight. We are able to enjoy God. It is a daily fight to keep both eyes on Jesus. If you are addicted to pornography, it is because you are not satisfied with Christ. Your main problem is not enjoying God. But brothers and sisters please do not just sit around until you enjoy God enough to forsake that sin. Flee from it. You are not fighting sin if you are not taking practical steps to put yourself in the best position to be overwhelmed by all God is for you in Christ. Don’t play will sin, because you should not treat joy lightly. There is more joy in obedience than there is sin. There is more grace in Christ than sin in you.

When we see the holiness of God it is transformative, as well fight to know and be satisfied by all God is for us in Christ, who has become both the just one and the justifier of the ungodly (you and me).