Yes, but. One possible answer to "What difference does it make?" is "I won't know until I answer the question." But that answer is better suited to physical sciences. (Let's mix this with that and see what happens.") We are in a position to see what Aquinas actually did with this question. Is there a place where he says 'BECAUSE law belongs to reason, ...." Or “BECAUSE law does not belong to reason, ...." That would be answer enough, if you can find it. Otherwise, to say he was "delving" or "examining" or "exploring" is just to say that he had no idea why he was doing so beyond "It seemed like a good idea at the time."

That Aquinas is not concerned with immediate decision making is my critique of his inquiry. He doesn't need to know what his inquiry will lead to next, but he must be able to say what it led to. Otherwise, the inquiry itself seems to have led him nowhere. If that is the case, I don't think it is wrong to criticize his approach. Indeed, it appears that the objections and responses try to say that "for purposes of" one thing, law does belong to reason and "for purposes of" something else, it doesn't. So why not ask "What role does reason play in the development of the law?"