The question “If Jesus pays for all your sins, then why not sin?” is an objection to grace anticipated by Paul in Romans 6:15: “Shall we sin because we are not under law but under grace? May it never be!” The objection reflects a misunderstanding of who Christians are as regenerated “new creatures” and how we view our new life in Christ.
Yes, Christians are justified because of the perfect work of Christ on the cross and His application of this work to us in His work as our high priest. His righteousness becomes our righteousness when we turn to Him and are united to Him through faith in Him and His work for us. We’re righteous because of His works, not ours. But that’s not all there is to understand about the relationship between Christians and sin.
When we trust in Christ to save us from the punishment we deserve, we are acknowledging our sinfulness and need for Him. Romans 6 explains that when we’re united to Christ, we’re “crucified with Him, in order that our body of sin might be done away with”—we die with Him, and then we’re raised with Him to a new life. Because of this, we’re to “consider ourselves to be dead to sin, but alive to God in Christ Jesus.”
We are new people now, no longer slaves to sin. We belong to Christ. Therefore, we’re told, “Do not go on presenting the members of your body to sin as instruments of unrighteousness; but present yourselves to God as those alive from the dead, and your members as instruments of righteousness to God.” We gave up our old bodies of sin when we died with Christ. Colossians 3 explains more:
Therefore if you have been raised up with Christ, keep seeking the things above, where Christ is, seated at the right hand of God. Set your mind on the things above, not on the things that are on earth. For you have died and your life is hidden with Christ in God...
Therefore consider the members of your earthly body as dead to immorality, impurity, passion, evil desire, and greed, which amounts to idolatry.
This is how Christians now view sin. We renounced it all when we died with Christ.
What shall we say then? Are we to continue in sin so that grace may increase? May it never be! How shall we who died to sin still live in it? Or do you not know that all of us who have been baptized into Christ Jesus have been baptized into His death? Therefore we have been buried with Him through baptism into death, so that as Christ was raised from the dead through the glory of the Father, so we too might walk in newness of life. (Romans 6:1-4)
At the same time, because we are still fallen in a fallen world, because our bodies have not been fully redeemed as they will be in the resurrection, everything we do is tainted by our sinful fallenness. This is why we’re told in 1 John 1:8-10, “If we say that we have no sin, we are deceiving ourselves and the truth is not in us. If we confess our sins, He is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness. If we say that we have not sinned, we make Him a liar and His word is not in us.”
This means that as we continue in our lives, fully justified because of receiving the forgiveness and righteousness of Christ through faith, and considering ourselves to be dead to sin, we will yet sin. When we do, we confess those sins, and He cleanses us from them. This is an ongoing part of our lives. To deny this is to call God a liar (see “Free to Say We’ve Sinned”). In other words, it’s not sinlessness that marks a Christian, it’s the attitude towards sin.
We rejoice in the grace that removes our guilt, but we don’t use it as an excuse for licentiousness. This is because, as Christians, our attitude towards sin has completely changed. We now hate it. We don’t cherish or protect sin. Instead, we confess it and ask for forgiveness. This is the attitude towards sin that has marked Christians from the beginning. In fact, both 1 John and Jude teach that we can recognize false Christians by their view of sin. “Ungodly persons who turn the grace of our God into licentiousness” are unequivocally condemned. They’re condemned as false Christians not because they’re not good enough to be Christians (no one is good enough to merit God’s grace!), but because their attitude towards sin proves they never died and rose with Christ. Those who have been changed by God and united to Christ will have a new view of sin. These are the ones who say with Paul, “Shall we sin because we are not under law but under grace? May it never be!”
To assume that Christians will use grace as an excuse to sin is to assume that Christianity is false—that God has not, in truth, called us “out of darkness into His marvelous light,” that we have not died with Christ and were not raised with Him as new creatures, that the old things have not passed away for us. It’s understandable that non-Christians would raise this objection, but it does not reflect the Christian view of our new life in Christ and our relationship to sin.