John Calvin Commentary Galatians 3:21

"Is the law then against the promises of God? God forbid: for if there had been a law given which could make alive, verily righteousness would have been of the law." — Galatians 3:21 (ASV)

Is the law then against the promises of God? The certainty and steadiness of the divine purpose being admitted, we are equally bound to conclude that its results are not contrary to each other. Still, there was a difficulty to be resolved, arising from the apparent contradiction between the Law and the covenant of grace. This is, perhaps, an exclamation. Dreading no further contradiction, now that the point is settled, Paul concludes that the former arguments have placed it beyond a doubt, and exclaims: “Who will now dare to imagine a disagreement between the law and the promises?” And yet, this does not prevent Paul from proceeding to remove the difficulties that might still arise.

Before answering the question, he expresses, in his usual manner, a high disdain for such folly, thus intimating the strong abhorrence with which pious men must regard whatever brings reproach on the Divine character. But another instance of high rhetorical skill, which claims our notice, is found in this turn of expression. He charges his adversaries with the offense of making God contradict Himself. For the Law and the promises have evidently proceeded from Him: whoever then alleges any contradiction between them blasphemes against God; but they do contradict each other if the Law justifies. Thus, Paul most dexterously retorts upon his adversaries the charge which they falsely and slanderously brought against him.

For if there had been a law given. The reply is (what is called) indirect and does not plainly assert an agreement between the law and the promises, but it contains all that is necessary to remove the contradiction. At first sight, you would say that this sentence departs from the context and has nothing to do with the solution of the question; but this is not the case. The law would be opposed to the promises if it had the power of justifying, for there would then be two opposite methods of justifying a man, two separate roads towards attaining righteousness. But Paul denies the law such a power, so the contradiction is removed. He says, “I would admit that righteousness is obtained by the law, if salvation were found in it.” But what?