The Power of Kaddish
“Rabbi Joshua ben Levi said: He who responds, יְהֵא שְׁמֵהּ רַבָּא מְבָרַךְ לְעָלַם וּלְעָלְמֵי עָלְמַיָּא ‘May His great Name be blessed forever and eternity’ with all his כֹּחַ might, his decreed sentence is torn up…
Resh Lakish said: He who responds ‘אָמֵן Amen’ with all his כֹּחַ might, has the gates of Paradise opened for him, as it is written, Open the gates, that the righteous nation which שֹׁמֵר אֱמֻנִים keeps the faith, may enter in [Isaiah 26:2]: read not שֹׁמֵר אֱמֻנִים shomer emunim ‘keeps the faith,’ but שֶׁאוֹמרִים אָמֶן she’omrim amen ‘that say, amen.’ What does ‘אָמֵן amen’ mean? — Said Rabbi Hanina: אֶל מֶלֶך נֶאֶמָן God, faithful King” (BT Shabbat 119b).
“Bezalel knew how to combine the letters with which God created heaven and earth [Genesis 35:3; BT Berakhot 55a]… and these are the twenty-eight letters of the verse בְּרֵאשִׁית בָּרָא אֱלֹהִים אֵת הַשָּׁמַיִם וְאֵת הָאָרֶץ [Genesis 1:1] about which it is said, the כֹּחַ power, of His deeds He told His people (Psalms 111:6) [כֹּחַ has a gematria of 28]. But at the time of the exile, these twenty-eight letters departed, as it is said: And they have gone without כֹּחַ strength, before the pursuer [Lamentations 1:6]. Therefore, it is said in [the introduction to] Kaddish ‘And now, may the כֹּחַ of the Lord be magnified,’ corresponding to twenty-eight other letters that [also] form seven words, which are יְהֵא שְׁמֵהּ רַבָּא מְבָרַךְ לְעָלַם וּלְעָלְמֵי עָלְמַיָּא ‘May His great Name be blessed forever and eternity.’ Thus, the [Sage’s] statement, ‘Whoever answers יְהֵא שְׁמֵהּ רַבָּא with all his כֹּחַ might, becomes a partner with the blessed Holy One in the work of Creation and the giving of the Torah’ [BT Shabbat 119b]” (Tiqqunei ha-Zohar 1:13a [72a]).