What shall we say then? — The Apostle had spoken in a manner disparaging to the Law, and which might well give offence to some of his readers. It was necessary to correct this. And so now he proceeds to lay down more precisely in what it was that the Law was defective, and what was its true function and relation to the history and struggles of humanity.
In what follows the Apostle speaks throughout in the first person. He is really making a general statement which applies to all mankind; but this statement is based upon his own personal experience. Self-analysis is at the bottom of most profound psychology. The Apostle goes back in thought to the time before he had embraced Christianity, and treats his own case as typical. There can be little question that the description which follows to the end of Romans 7:24 is a description of the unregenerate state of man. It is one prolonged crisis and conflict, which at last finds its solution in Christ.
Is the law sin? — The Law had just been described as stimulating and exciting “the motions of sins.” Was this true? Was the Law really immoral? No, that could not be.
Nay. — Rather, howbeit (Ellicott), nevertheless. The Law is not actually immoral, but it is near being made so. It is not itself sin (sinful), but it reveals, and so in a manner incites to, sin.
I had not known. — Strictly, I did not know. I had no acquaintance with sin except through the Law. Before the introduction of law, acts that are sinful in themselves, objectively viewed, may be done, but they are not sinful with reference to the person who does them. He has no knowledge or consciousness of what sin is until it is revealed to him by law.
Sin. — Here a sort of quasi-personification. The principle or power of sin into contact and acquaintance with which the Apostle was brought for the first time by the Law.
I had not known lust. — The Apostle introduces an illustration from a special law — the Tenth Commandment. “Lust” is here to be taken in the special sense of covetousness, desire for that which is forbidden. Doubtless there would be many before the giving of the Law who desired their “neighbour’s wife, or his manservant, or his maidservant,” &c.; but this would not be coveting, it would not be desire of that which was forbidden, for the simple reason that it was not forbidden. Covetousness, then, as a sin, the Apostle did not know until he was confronted with the law against it.