In our passage for study Paul explains that a person can be subject to only one of two masters; we are either a slave to sin promoting ever-increasing wickedness unto death, or a slave to God promoting an abundance of right-living unto life eternal.
v15. As in verse 1, Paul outlines a criticism made against him by law-bound believers. These believers were critical of Paul's claim that a person appropriates the fullness of God's promised blessings because of Christ's faithfulness, and this apart from law-obedience. They felt that Paul's teaching promoted careless-living in the Christian life, inevitably undermining a person's holiness and thus their blessings in Christ. Their argument, evident in this verse, is that Paul devalues sin. "No way", says Paul; living under God's grace, rather than his law, promotes right conduct, not sin.
v16. Sinful living, or right living, depends on the master we serve, whether sin or obedience. If we live in the sphere of sin, our end is death; if we live in the sphere of obedience, our end is righteousness, right-standing in the sight of God.
v17-18. Paul is thankful that his readers have heard the gospel and therefore are transferred from the domain of sin where they lived in rebellion against God, to the domain of righteousness, "the gracious power of God which claims and sustains the believer and reaches its final expression in eternal life", James Dunn.
v19a. At this point Paul qualifies his use of the slavery image. A Christian's relationship to God is not at all unjust, humiliating and degrading, as is slavery; it is a service of perfect freedom - liberation.
v19b. So, as free men and women, Paul reminds his readers that as they once served the domain of sin to ever-increasing wickedness, they should now serve the domain of God's saving grace leading to holiness - a state of purity before God expressing itself in purity of life. Willy-nilly sinning is not the fruit of grace.
v20-21. When they served the domain of sin they couldn't live a righteous life; their end was death - death to God, death eternal.
v22. But now, set free from the domain of sin and death and incorporated into the domain of God's righteousness and grace, the fruit that flourishes is holiness and life eternal.
v23. In summary then, the end of sin is greater and greater iniquity leading to death, the end of grace is holiness leading to life eternal.
Believers have always found it difficult to accept the notion of God's free grace, apart from law-obedience, because it seems to ignore sin. If a believer has already been gifted with perfect righteousness for eternity, if all their good works, all their faithfulness to the law of God, cannot in any way add to their standing before God, cannot in any way access any more of God's love for them than they already possess, then why worry about sin? Why try to do well? Why strive to live a righteous life? Why get fussed by a few sins here or there?
The truth is that not only does our faith in Christ's faithfulness on our behalf gain God's eternal approval for us, but it results in obedience rather than disobedience; it results in right conduct. Sure, we will fail, and sometimes fail badly, but our whole orientation is toward being the person we are already in Christ. So, in simple terms, free grace never means free sin.
If there is nothing we can do to make God either love us more or less, why bother trying to please him?