John Calvin Commentary Romans 9:31

"but Israel, following after a law of righteousness, did not arrive at [that] law." — Romans 9:31 (ASV)

But Israel, by pursuing, etc. Paul openly states what seemed incredible — that it was no wonder the Jews gained nothing by diligently pursuing righteousness, for by running astray, they wearied themselves in vain. But in the first place, it seems to me that the law of righteousness is here an instance of transposition and means the righteousness of the law. Then, when repeated in the second clause, it should be understood in another sense, signifying the model or the rule of righteousness.

The meaning then is — “That Israel, by depending on the righteousness of the law, even that which is prescribed in the law, did not understand the true method of justification.” But there is a striking contrast in the expression when he teaches us that legal righteousness was the cause of their falling away from the law of righteousness.