John Calvin Commentary Romans 6:20

"For when ye were servants of sin, ye were free in regard of righteousness." — Romans 6:20 (ASV)

For when you were, etc. He still repeats the difference, which he had previously mentioned, between the yoke of righteousness and that of sin; for these two things, sin and righteousness, are so contrary that whoever devotes himself to the one necessarily departs from the other. And he represents both in this way, so that by viewing them separately, we may see more clearly what is to be expected from each; for setting things apart in this way enables us to understand their distinctive character better. 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.

Let us then remember that the Apostle still reasons on the principle of contraries, and in this manner, “While you were the servants of sin, you were freed from righteousness; but now that a change has taken place, it is fitting for you to serve righteousness, for you have been liberated from the yoke of sin.” He calls those free from righteousness who are held by no bridle to obey righteousness. This is the liberty of the flesh, which so frees us from obedience to God that it makes us slaves to the devil. Wretched then and accursed is this liberty, which with unbridled or rather mad frenzy, leads us exultingly to our destruction.