Immediately following the first verse, we say quietly, “Baruch shem kevod malchuto l’olam va’ed,” (“Blessed is the name of His glorious kingdom for all eternity”). Although this sentence does not appear with the Shema paragraph and is not a verse from the Torah, the Chachamim instituted its recital as part of Shema based on ancient tradition.
It is told in the Talmud (Pesachim 56a) that before Yaakov Avinu died, all of his children gathered around him. Yaakov wished to reveal the end of days, but at that moment the Shechinah left him and he could not show them the future. He asked his sons, “Perhaps one of you is not righteous, like Yishmael, who came from Avraham, and Eisav, who came from my father Yitzchak, and that is preventing me from revealing to you the end of days?” Everyone opened their mouths and said, “‘Hear O Israel, Hashem is our God, Hashem is One.’ Just like there is only One in your heart, there is only One in our hearts.” At that moment, Yaakov said, “Blessed is the name of His glorious kingdom for all eternity.” Chazal ask, “Now what should we do? Should we recite this sentence [in Shema] even though it is not written in the Torah portion? Or should we refrain from saying it even though Yaakov Avinu said it?” Therefore, they established to recite it quietly.
This sentence is considered to be a continuation of the acceptance of the yoke of Heaven found in the first verse, and therefore also requires kavanah on the meaning of the words. If a person recites it without the proper kavanah he must go back and repeat it with the proper kavanah (Mishnah Berurah 63:12).
One should pause briefly between “l’olam va’ed” (“for all eternity”) and “V’ahavta” (“You shall love”) in order to distinguish between the acceptance of the yoke of Heaven and the rest of the paragraph. Also, it is proper to pause between the first verse and “Baruch shem” (“Blessed be the name…”) to differentiate between the acceptance of the yoke of Heaven as commanded by the Torah and the enactment of the Chachamim (Shulchan Aruch and Rama 61:14).
Although the belief in the oneness of God holds unfathomable depths and meanings, we will nonetheless briefly discuss its significance. The first verse, Shema Yisrael, expresses the absolute and unifying higher belief and is called “yichud elyon” (the supernal unification). In this realm of higher understanding, nothing else substantially exists in the world besides Hashem. He is One in His world, and we are all insignificant in relation to Him. Since Hashem’s infinite power is not visible to us, it is difficult to grasp the supernal union permanently. Therefore, only twice daily, when we recite the verse Shema Yisrael, are we commanded to rise to its level. The second verse is called “yichud tachton” (the lower unification), and by saying it, we accept upon ourselves the yoke of Heaven according to the belief that is revealed in this world. This is the belief that the world is not void, rather tangible and existent, and Hashem Blessed Be He gives it life and rules over it. By His will He creates life, or God forbid, takes it away. In so doing, His Name and kingdom are revealed in the world, as we say, “Blessed is the name of His glorious kingdom for all eternity” (Tanya, Sha’ar HaYichud V’HaEmunah, and Nefesh HaChaim, Sha’ar 3).