The fact that all sin committed by believer is justified by the grace of God through Christ's death, does not give him license to continue living in sin.
The previous chapters of Romans describe how all humankind is sinful because of the original sin of Adam, and how God has provided justification by the death of one man, his son Jesus Christ. This is the measure of God's grace, which provides forgiveness to whosoever repents of his sin and seeks Him.
In fact, this is the core of the Gospel of Christ, which has been preached and received by millions of people for almost two millennia.
However, there has been strong opposition to it by religious theorists since very early times, especially the Jews. They all insist that man himself can and must be justified by his own works, and that the Gospel of Christ cannot be true because it makes justification too easy, and even unjust according to their philosophies.
Their basic argument has been that, if the sinner is pardoned by means of a simple conversion to Christ, disregarding the severity and volume of his sins, then the measure of God's grace varies depending on the volume of sin; this is an incentive for believers to sin even more, so God may reveal even more of His grace within His unlimited pardon.
However, does the Gospel (salvation by grace through faith only) really allow or even encourage the believer to live in sin? The second verse of this passage consists of a strong "certainly not! ", given by the Apostle Paul to this argument. Then he explains why not, and discourses until chapter 8 on the sanctification of the believer following his conversion.
When a sinner becomes a believer, he is saved from the penalty and power of sin through his faith in Jesus Christ, and dedicates his new life to follow Christ and to serve God. His sinful life dies, it is buried and undone forever just as Christ died on the cross and was buried. He is spiritually united with Christ, born again as a new spiritual creature to live forever, just as Christ rose from the grave in a new glorious body, to return to the presence of God.
This death, burial and resurrection of the believer are symbolised by the immersion and lifting out of his body from water (baptism), whereby the believer gives his testimony to those present.
He should not ignore (v. 3), but know (v. 6, 9) that his new situation is as follows:
In this new situation, the believer by God's grace having acquired a position of perfection, with eternal and total exemption of sin, will live in a way worthy of it here in the world. In addition, by the grace of God, he is taught how to follow His way and to live accordingly.
The contrast between the two situations can be seen better like this:
The believer knows that sin has no more hold on him, because he has died to sin and received the Holy Spirit in his life, which gives him the power to live a Holy life. He is no longer under the law but grace. The law told him what to do, but did not give him the power to meet its demands. It even woke him to desires and lusts in his "body of sin" for what was forbidden – he saw the forbidden fruit as being "pleasing to the eyes and good for eating".
In his new life, the believer is motivated by love for the Saviour, not by fear of punishment. The grace of God produces holiness of life through the action of the Holy Spirit in the believer that fills himself with Him.
It is the grace of God that places the believer in his new situation, then teaches him to live in a way worthy of it. The position in which he now finds himself is perfect because he is in Christ. The believer will not take advantage of it to sin again, having already learned that anyone who disobeys God places himself under sin for death, but who is obedient is made a servant of justice.
His way of living should correspond increasingly to the position in which he finds himself. The believer is free of the law, but is not unruly. Grace gives freedom to live to serve the Lord, but not to sin against Him. The question in verse 15 can be understood as, "can we sin just a little bit?" but the answer is "not at all". God cannot pass over any sin, however small it is. As the servant of God, the believer cannot again serve sin.
Before his conversion, man is a slave of sin, and "is free in regard to righteousness " (v. 20). This means that he does not feel an obligation to practice justice. He practises sin and finds himself sentenced to death for it – so why practise justice?
The believer will not come to perfection until he meets the Saviour in heaven, but meanwhile he will increasingly conform to His image here.
Returning to the original question, in short what we learn here in suggests four appropriate responses:
1 What shall we say then? Shall we continue in sin that grace may abound?
2 Certainly not! How shall we who died to sin live any longer in it?
3 Or do you not know that as many of us as were baptized into Christ Jesus were baptized into His death?
4 Therefore we were buried with Him through baptism into death, that just as Christ was raised from the dead by the glory of the Father, even so we also should walk in newness of life.
5 For if we have been united together in the likeness of His death, certainly we also shall be in the likeness of His resurrection,
6 knowing this, that our old man was crucified with Him, that the body of sin might be done away with, that we should no longer be slaves of sin.
7 For he who has died has been freed from sin.
8 Now if we died with Christ, we believe that we shall also live with Him,
9 knowing that Christ, having been raised from the dead, dies no more. Death no longer has dominion over Him.
10 For the death that He died, He died to sin once for all; but the life that He lives, He lives to God.
11 Likewise you also, reckon yourselves to be dead indeed to sin, but alive to God in Christ Jesus our Lord.
12 Therefore do not let sin reign in your mortal body, that you should obey it in its lusts.
13 And do not present your members as instruments of unrighteousness to sin, but present yourselves to God as being alive from the dead, and your members as instruments of righteousness to God.
14 For sin shall not have dominion over you, for you are not under law but under grace.
15 What then? Shall we sin because we are not under law but under grace? Certainly not!
16 Do you not know that to whom you present yourselves slaves to obey, you are that one's slaves whom you obey, whether of sin leading to death, or of obedience leading to righteousness?
17 But God be thanked that though you were slaves of sin, yet you obeyed from the heart that form of doctrine to which you were delivered.
18 And having been set free from sin, you became slaves of righteousness.
19 I speak in human terms because of the weakness of your flesh. For just as you presented your members as slaves of uncleanness, and of lawlessness leading to more lawlessness, so now present your members as slaves of righteousness for holiness.
20 For when you were slaves of sin, you were free in regard to righteousness.
21 What fruit did you have then in the things of which you are now ashamed? For the end of those things is death.
22 But now having been set free from sin, and having become slaves of God, you have your fruit to holiness, and the end, everlasting life.
23 For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.
Romans chapter 6