Reish Lakish taught that when Yaakov Avinu called his children to his deathbed to reveal their future, the Shechina suddenly departed from his presence. When he expressed concern that this was due to perhaps one of his offspring being unfit, his children assured him that “Hear O Israel (their father’s name), Hashem is our G-d, Hashem is One! Just as in your heart there is only one Hashem, likewise in our hearts there is only one Hashem!” When Yaakov heard their words of loyalty to Hashem, he responded with the words, “Baruch Shem Kavod Malchuto L’Olam Va’ed — Blessed is the Name of His glorious Kingdom for all eternity!”

The gemara relates that our Sages were faced with a dilemma regarding the saying of Baruch Shem Kavod immediately after we say Shema Yisrael in our daily prayers. They deliberated: “Should we say it? Perhaps not, because Moshe Rabbeinu did not write it in the Torah. Should we not say it? Perhaps yes, because Yaakov said it upon hearing his children say Shema Yisrael.” Our Sages reached a decision and decreed that we should indeed say Baruch Shem Kavod — but that we should say it quietly. And, this is, in fact, the manner that we say the Shema with Baruch Shem Kavod nowadays, everywhere.

The conclusion in our gemara to say Baruch Shem Kavod quietly is qualified by Rabbi Abahu. He said that there is a difference when the Shema is being said in a place where heretics are prevalent. In such a place, Baruch Shem Kavod should be said aloud, and not quietly, so that a person would not be suspected of making a quiet disclaimer to his previous announcement that “Hashem is One.” The gemara adds that in a place such as Nahardai, where heretics did not exist, it should be said quietly, in accordance with the conclusion of our Sages’ deliberation.

The classical Torah commentaries raise a question on what is taught on our daf from another teaching that we learn elsewhere in Shas (Berachot 12a). There we are taught that the Sage Ameimar wanted make a decree for the people of (this same place called) Nahardai to say the Ten Commandments each day, in addition to the Shema, as part of the public prayer service. However, he decided not to institute it, out of his concern that the heretics would claim that only these commandments — which the Jewish People heard when Hashem gave us His Torah at Mount Sinai — constitute the entirety of the Torah.

This apparently contradicts what we learn on our daf. If, in Nahardai (and other non-heretical places), due to the lack of heretics there, Baruch Shem could and should be said quietly, why was Ameimar concerned about saying the Ten Commandments in Nehardai out of fear of what the heretics might claim?

One answer to resolve this question is to distinguish between the degrees of danger of heresy that exist in these two cases. Singling out the Ten Commandments posed the danger of being misleading about the essence of the Torah and the truth of the entire Torah. This concern was so great that this practice was banned everywhere. However, the concern that quietly saying Baruch Shem… might be wrongly seen as a heretic’s disclaimer is relatively remote. It is a lesser degree of danger, as it were. Therefore, this whispered praise was not banned in Nahardai and the like, but only in places that were ripe with heresy, where it needed to be said aloud. (Rashash)

It is worthwhile to note that, in addition to the reason cited in our gemara for saying Baruch Shem Kavod quietly, we find another reason for this practice in the Midrash. Moshe Rabbeinu heard this beautiful prayer from the angels and taught it to the Jewish People. However, we do not say it aloud since we are sinful and thus unworthy of uttering this angelic formula. But, on Yom Kippur, when the Jewish People is elevated to the sinless nature of the angels, we may say Baruch Shem Kavod aloud. (Devarim Rabbah 2:36)