Some misinterpret the Apostle Paul’s teaching in Romans 5:20, which states, “Where sin increased, grace increased all the more.” A number of people take this verse to mean that Christians can live the way they want without consequences. Many who misinterpret this verse fail to see that this claim leads to a question Paul asks in Romans 6:1, which he answers in 6:2. He affirms, “What shall we say then? Shall we go on sinning so that grace may increase? By no means! We are those who have died to sin; how can we live in it any longer? He continues by stating, “For we know that our old self was crucified with him so that the body ruled by sin might be done away with, that we should no longer be slaves to sin" (Romans 6:6). When commenting on these verses R.C. Sproul asserts, “(Paul) makes the point that to continue in sin would involve a contradiction of the Christian’s new identity in Christ.”
Freedom for a believer in Christ means that one is free from the rule of sin and its consequences. Paul states, "Anyone who has died has been set free from sin. Now if we died with Christ, we believe that we will also live with him. For we know that since Christ was raised from the dead, he cannot die again; death no longer has mastery over him" (Romans 6:7-9). Not only is the rule of sin eliminated, but the sting of death is removed because everyone who is trusting in Christ for their salvation will overcome the second death, which is the penalty for sin (Romans 6:23), and will be raised from this life to spend eternity in the presence of the Lord.
Since believers have been freed from the rule of sin, it does not make since to Paul that one would allow sin to regain control. He asserts, "Therefore do not let sin reign in your mortal body so that you obey its evil desires. Do not offer any part of yourself to sin as an instrument of wickedness, but rather offer yourselves to God as those who have been brought from death to life; and offer every part of yourself to him as an instrument of righteousness. For sin shall no longer be your master, because you are not under the law, but under grace" (Romans 6:12-14). According to Sproul, "In view of this new identity (v.11), Christians are to refuse to allow sin to usurp authority in their lives, and instead are to yield the whole of life to God (vv. 12, 13) in the assurance that since they are under grace, not law, as the means of their salvation, sin is no longer their master."
Romans. The Reformation Study Bible. Edited by R.C. Sproul, pp. 1621-1622.