Question

To the honored Rabbi,
Greetings and blessings.
I hope I’m not bothering you…. I tried searching the site to see whether the Rabbi had already answered the following question and didn’t find it….
I’m trying to clarify the topic of a stolen Megillah, regarding which it is ruled in the Shulchan Arukh that one does fulfill the obligation, and this comes from a responsum of the Rashba who compared it to a shofar.
What I’m trying to understand is this:
Why is it that with shofar, on the one hand, we recite the blessing “to hear the sound of the shofar,” and so it seems that the commandment is hearing the sound; yet on the other hand, we still deal with who is blowing, that it should not be a minor or a woman—that is, someone obligated in the matter—or that he should intend to blow in order to discharge others of their obligation, and so on?
Why, if we say that the commandment is hearing the sound, do we still require all sorts of parameters regarding the manner of the blowing?
As for the laws of the shofar itself, I can understand that invalidations of the shofar are connected to the required sound, and if the shofar is cracked, even though a shofar sound came out, that is not the sound we mean.
But regarding the requirements for the blower and the blowing, I don’t understand why that is necessary.
And I’m not asking from the perspective of the essence of the commandment being hearing the sound, but rather as an internal contradiction: what is the idea behind permitting hearing the sound of a stolen shofar on the grounds that the commandment is hearing the sound, while at the same time requiring parameters regarding the blower?
I think this is quite a fundamental question, also for understanding the commandment of shofar, Megillah, and other commandments.
Thank you very much.