John Calvin Commentary Romans 7:21

"I find then the law, that, to me who would do good, evil is present." — Romans 7:21 (ASV)

I find then, etc. Here Paul supposes a fourfold law. The first is the law of God, which alone is properly so called, and which is the rule of righteousness by which our life is rightly formed. To this he joins the law of the mind, by which he means the prompt readiness of the faithful mind to render obedience to the divine law, this being a certain conformity on our part with the law of God. On the other hand, he sets in opposition to this the law of unrighteousness; and by a certain similarity, he gives this name to the dominion that iniquity exercises over a person not yet regenerated, as well as over the flesh of a regenerated person. For even the laws of tyrants, however wicked they may be, are called laws, though not properly. To correspond with this law of sin, he names the law of the members, that is, the lust which is in the members, because of the concord it has with iniquity.

Regarding the first clause, many interpreters take the word law in its proper sense and consider κατὰ or διὰ to be understood; and so Erasmus renders it, “by the law,” as though Paul had said that he, by the law of God as his teacher and guide, had found out that his sin was innate. But without supplying anything, the sentence would read better as follows: “While the faithful strive after what is good, they find in themselves a certain law that exercises a tyrannical power, for a vicious propensity, adverse to and resisting the law of God, is implanted in their very marrow and bones.”