The Talmud relates the origin of the inclusion of “Barukh Shem K’vod Malkhuto L’Olam Va’ed” in the recitation of K’riat Shma. Ya’akov, toward the end of his life, wished to share with his offspring the date of the future redemption. However, the knowledge left him, and he feared that this indicated he had unworthy offspring. They reassured him by reciting the sentence of “Shma Yisrael”, conveying the message that “just as in your heart there is only One, so too in our hearts there is only One.” He responded with “Barukh Shem K’vod Malkhuto”. The Talmud then notes that the Rabbis were unsure how to relate to this phrase within Kriat Shma: on the one hand, Moshe did not say it; on the other, Ya’akov did. The resolution was to say it in a whisper. The Maharam Shick (Maharam Shick al haTorah, Bereishit, pp. 178-180) explains that Ya’akov’s statement of “Barukh Shem K’vod Malkhuto” represents his awareness that even at the moment of death, he is not afraid, because the reality of G-d’s everlasting glory is reassurance of the eternal good of G-d’s creation. The Rabbis were unsure as to whether or not to include this in K’riat Shma, because Moshe had omitted it, due to the fact that the Torah is a book of commandments to be observed in and of themselves, and not due to promise of eternal protection. However, the Rabbis realized that people need the encouragement, and thus instituted that it should be recited quietly. (It should be noted that the Maharam Shick actually explains this passage at least four different ways; see also Maharam Shick al haTorah, Devarim, p. 191; p. 214; and p. 224; see also his extensive discussion in Bereishit, ibid.). From a halakhic perspective, the Maharsha explains the concern of the Talmud regarding the insertion of a non-Mosaic sentence into K’riat Shma as a possible slight against Moshe, by adding to his words in a loud voice. The quiet recitation thus minimizes the slight. The Tzlach, however, understands the issue as one of an impermissible “hefsek” (interruption) between Shma and “V’Ahavta”, and thus derives from the Talmud’s conclusion that a whispered statement does not constitute a hefsek. R. Eliezer Silver (as cited by R. Shlomo Wharman, Sh’erit Yosef, II, p. 43) uses this idea to explain the view of Rashi (Sukkah 38b) that one who is in the middle of the silent Amidah when the congregation is reciting Kaddish or Kedushah should stop and listen quietly, thus answering through the mechanism of shomea k’oneh. Tosafot (Berakhot 21b) objects, noting that if listening really counts as speaking, then even listening would constitute a hefsek. However, according to the Tzlach’s position, it emerges that only words spoken out loud constitute a hefsek. R. Wahrman (ibid, p. 44-5) continues to explain that this view might clarify the position of the Rokeach (Hil. Shabbat, 49) that “v’shamru” on Friday night should be recited quietly. Commentaries debate the permissibility of reciting anything at all at that point in davening, which would constitute an interruption between the berakhah of geulah and the amidah (see Tur O.C. 267). Based on the Tzlach, it may be that the Rokeach’s position is that a statement made quietly avoids problems of hefsek. The Arukh HaShulchan (O.C. 25:13) suggests that the Talmud’s story may play a role in the halakhic practice of donning tefillin. Prevalent Ashkenazi practice is to recite two berakhot on tefillin: “l’honiach” before the “shel yad”, and “al mitzvat Tefillin” before the “shel Rosh”. Following the second berakhah, “Barukh Shem K’vod Malkhuto L’Olam Va’ed” is then recited The common explanation of this practice is based on the fact that there is a disagreement among halakhic authorities as to whether both berakhot should actually be recited under normal circumstances. Thus, “Barukh Shem” is recited to negate any unjustified invocation of G-d’s Name. The Arukh HaShulchan, acknowledging that the above explanation is standard, offers a completely different explanation. It is indeed unusual for one mitzvah to have two berakhot. Rather, the first berakhah is the “birkat ha-mitzvah” and the second berakhah is a berakha of praise, expressing our gratitude for the special relationship the Jewish people has with G-d. That relationship is represented by the tefillin, which are paired with K’riat Shma. The story with Ya’akov teaches that the correlate to “Shma Yisrael” is “Barukh Shem”; thus, that phrase is especially appropriate in this context. The poskim discuss the question of whether “Barukh Shem” is considered an integral part of K’riat Shma. As R. Avraham Weinfeld (Resp. Lev Avraham, 11) clarifies, this question can only be posed on a rabbinical level, as the phrase clearly does not appear in the biblical text. However, he also acknowledges the possibility, debated by authorities, that failing to perform a mitzvah in the manner mandated by the Rabbis can invalidate the mitzvah on a biblical level as well. The Magen Avraham (61:11) quotes opinions that one who omits “Barukh Shem” does not need to repeat K’riat Shma, but sides with the view of the Levush that one must repeat K’riat Shma even if Barukh Shem was said but with insufficient concentration. (See also Resp. Iggerot Moshe, O.C. V, 5:3.)