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 [koaḥ] might, his decreed sentence is torn up…
Resh Lakish said: He who responds ‘אָמֵן Amen’ with all his כֹּחַ [koaḥ] might, has the gates of Paradise opened for him, as it is written, Open the gates, that the righteous nation which שֹׁמֵר אֱמֻנִים [shomer emunim] 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, אֶמָן [amen] amen. What does ‘אָמֵן [amen] 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 [koaḥ] power, of His deeds He told His people (Psalms 111:6) [כֹּחַ has a numerical value of 28]. But at the time of the exile, these twenty-eight letters departed, as it is said: And they have gone without כֹּחַ [koaḥ] strength, before the pursuer [Lamentations 1:6]. Therefore, it is said in [the introduction to] Kaddish ‘And now, may the כֹּחַ [koaḥ] 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 [yeheh shemeh rabba mevarakh le-alam ul-alemei alemaya] May His great Name be blessed forever and eternity. Thus, the [Sage’s] statement, ‘Whoever answers יְהֵא שְׁמֵהּ רַבָּא [yeheh shemeh raba] May his great Name, with all his כֹּחַ [koaḥ] 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]).