Paul writes to the church in Rome:

I am speaking in human terms, because of your natural limitations. For just as you once presented your members as slaves to impurity and to lawlessness leading to more lawlessness, so now present your members as slaves to righteousness leading to sanctification.

For when you were slaves of sin, you were free in regard to righteousness. But what fruit were you getting at that time from the things of which you are now ashamed? For the end of those things is death.

But now that you have been set free from sin and have become slaves of God, the fruit you get leads to sanctification and its end, eternal life. For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord.

Romans 6:19-23 English Standard Version (ESV)

The Westminster Confession Shorter Catechism Question and Answer number 35 states:

What is sanctification? Sanctification is the work of God’s free grace, whereby we are renewed in the whole man after the image of God, and are enabled more and more to die unto sin, and live unto righteousness.

What does John Calvin say about these verses in Romans here and here?

I speak what is human, etc. He says that he speaks after the manner of men, not as to the substance but as to the manner. So Christ says, in John 3:12, that he announced earthly things, while yet he spoke of heavenly mysteries, though not so magnificently as the dignity of the things required, because he accommodated himself to the capacities of a people ignorant and simple.

…As though [the Apostle] had said, “I might, by comparing sin and righteousness, show how much more ardently you ought to be led to render obedience to the latter [righteousness], than to serve the former [sin]; but from regard to your infirmity I omit this comparison: nevertheless, though I treat you with great indulgence, I may yet surely make this just demand — that you should not at least obey righteousness more coldly or negligently than you served sin…”

As you have presented, etc.; that is, “As you were formerly ready with all your faculties to serve sin, it is hence sufficiently evident how wretchedly enslaved and bound did your depravity hold you to itself: now then you ought to be equally prompt and ready to execute the commands of God; let not your activity in doing good be now less than it was formerly in doing evil.” He does not indeed observe the same order in the antithesis, by adapting different parts to each other, as he does in 1 Thessalonians 4:7, where he sets uncleanness in opposition to holiness; but the meaning is still evident…

For when you were, etc. He still repeats the difference, which he had before mentioned, between the yoke of righteousness and that of sin; for these two things, sin and righteousness, are so contrary, that he who devotes himself to the one, necessarily departs from the other. And he thus represents both, that by viewing them apart we may see more clearly what is to be expected from each; for to set things thus apart enables us to understand better their distinctive character. He then sets sin on one side, and righteousness on the other; and having stated this distinction, he afterwards shows what results from each of them…

What fruit, then, etc. He could not more strikingly express what he intended than by appealing to their conscience, and by confessing shame as it were in their person. Indeed the godly, as soon as they begin to be illuminated by the Spirit of Christ and the preaching of the gospel, do freely acknowledge their past life, which they have lived without Christ, to have been worthy of condemnation; and so far are they from endeavoring to excuse it, that, on the contrary, they feel ashamed of themselves. Yea, further, they call to mind the remembrance of their own disgrace, that being thus ashamed, they may more truly and more readily be humbled before God…

Ye have your fruit unto holiness, etc. As he had before mentioned a twofold end of sin, so he does now as to righteousness. Sin in this life brings the torments of an accusing conscience, and in the next eternal death. We now gather the fruit of righteousness, even holiness; we hope in future to gain eternal life. These things, unless we are beyond measure stupid, ought to generate in our minds a hatred and horror of sin, and also a love and desire for righteousness…

For the wages of sin, etc. …This verse is a conclusion to the former, and as it were an epilogue to it. He does not, however, in vain repeat the same thing again; but by doubling the terror, he intended to render sin an object of still greater hatred.

But the gift of God. They are mistaken who thus render the sentence, “Eternal life is the gift of God,” as though eternal life were the subject, and the gift of God the predicate; for this does not preserve the contrast. But as he has already taught us, that sin produces nothing but death; so now he subjoins, that this gift of God, even our justification and sanctification, brings to us the happiness of eternal life. Or, if you prefer, it may be thus stated, — “As the cause of death is sin, so righteousness, which we obtain through Christ, restores to us eternal life…”

I Could Laugh (feat. Chris Taylor) performed at BD’s House, 2014, by Michael Roe