Question

Following up on the previous question, Eruvin 78 / Sabbath 132, I have another question about the derivations there. (So many homiletic expositions on one page—what a pleasure…) The Talmud there refutes an a fortiori argument, saying that sounding the shofar is more stringent because it brings the remembrances of Israel before their Father in Heaven. And likewise circumcision is more stringent because thirteen covenants were made concerning it. And it is difficult: A. Do “faith-based” considerations make a law more stringent, such that one can no longer derive from it by an a fortiori argument? B. Fine—those covenants regarding circumcision were written explicitly, and many times. But that the shofar brings in remembrances is not stated explicitly anywhere in the Torah; it only says “a memorial of teruah.” On what basis would we say it is more stringent because of that? How does the stirring homily before the shofar blasts become a halakhic “there is” in the legal sense? I thought one could say that a refutation of an a fortiori argument only needs to be somewhat plausible, and the burden of proof is on the one innovating a law through an a fortiori argument to show that it is airtight. Therefore any refutation is effective.