The daily mitzva of accepting the yoke of heaven is fulfilled primarily by declaiming the verse, “Hear, O Israel! The Lord is our God, the Lord is one” (Devarim 6:4). We immediately follow this with the quiet recitation of the sentence, “Blessed be the name of His glorious kingdom forever and ever (Barukh shem kevod malkhuto le-olam va-ed).” Even though this sentence does not appear in the portion of Shema, or in the Torah at all, the Sages ordained its silent recitation (Peninei Halakha: Prayer 15:7 n. 1). The Talmud recounts the origin of this sentence: Before our patriarch Yaakov died, he gathered all his sons around him and wanted to reveal to them the end of days, but the Divine Presence left him. He said to his sons, “Perhaps one of you is not worthy. After all, Avraham had Yishmael, and Yitzḥak had Esav. Is that why I cannot reveal the end to you?” They responded by declaring unanimously, “‘Hear, O Israel! The Lord is our God, the Lord is one.’ Just as the one God alone is in your heart, so too, the one God alone is in our heart.” At that point Yaakov said, “Blessed be the name of His glorious kingdom forever and ever.” This story posed a dilemma to the Sages: What to do? Should we recite the sentence? It does not appear in the Torah! Yet how can we not recite it? Our patriarch Yaakov said it! Therefore, they ordained that it be recited quietly. “This is like a princess who smelled food stuck to the bottom of the pot (and craved them). If she were to admit to the craving, she would embarrass herself; if she were to say nothing, she would miss out. So her servants started sneaking them to her” (Pesaḥim 56a).
Another tradition maintains that Moshe Rabbeinu ordained this recitation. When he ascended to heaven, he heard the ministering angels praising God by saying, “Blessed be the name of His glorious kingdom forever and ever.” Upon his descent, Moshe ordained that the Jews recite it quietly. The question was raised: Why did he not ordain that they recite it aloud? A parable was offered in response: To what can this be compared? To a confidant of the king who stole a very nice cloak from the royal palace and gave it to his wife, saying, “Do not wear this in public; only at home.” Only on Yom Kippur, when Israel is as pure as the ministering angels, may they recite it aloud (Devarim Rabba 2:36).
To understand the meaning of these ideas, we must first explain two levels of faith in one God. The first statement, the Shema, expresses the highest level of absolute unification, referred to as yiḥud elyon (“higher unification”). At this level, every aspect and detail unites to reveal God. The second statement, Barukh shem kevod, expresses the plane which came into being after the world’s creation, referred to as yiḥud taḥton (“lower unification”). This involves acceptance of the yoke of heaven based on God’s manifestation in this world, where every creature and every aspect has a real place; God gives them all life and rules over them in accordance with their deeds. This is called the revelation of His name (shem) and kingship (malkhut). That is, His name and His governance are manifest in the world, but not His essence. If He would reveal His essence, all of creation would be annulled and melt away before His great light. (See Tanya, Sha’ar Ha-yiḥud Ve-ha’emuna.)
The higher level of faith is extremely lofty, revealed only at the root of the soul and only at times of self-sacrifice. Accordingly, we are commanded to tap into yiḥud elyon only twice a day, with the recitation of Shema. The Sages ordained pairing it with yiḥud taḥton, which acknowledges God’s manifestation within this diverse world. (See Nefesh Ha-ḥayim 3.) Yiḥud taḥton is very precious to God, as the purpose of creation is for God to be recognized within this material world, with all its beauty and glory, colors and sounds, urges and inclinations. Thus, the ministering angels praise God with the amazing paean, “Blessed be the name of His glorious kingdom forever and ever.” However, saying it out loud is improper, because alongside the positives of revealing the Divine Presence in this world, there are also negatives – evil impulses that can draw us to sin. Therefore, one must first connect to yiḥud elyon and only then quietly recite the praise of yiḥud taḥton, to avoid the temptations of this world.
Only on Yom Kippur, as we fast and desist from occupation with our bodily needs, to the extent that we become like ministering angels, impervious to the evil inclination, can we utter Barukh shem kevod aloud, knowing that we are privileged to sanctify His name in this world. Even though we sometimes stumble into sin, on Yom Kippur it is revealed that ultimately, we draw down His light into this world, in all its complexity. As a result, God judges the Jews with love and mercy. (See Derekh Hashem 4:4:6-7.)