Musar do Kapłańska 22:33

9) When one prays with the congregation, he has [the opportunity of saying] Barchu, Kedushah, and Amen yehei shemei rabbah, each of which, in itself, is awesome. For through "Barchu" we make a crown for the Holy One Blessed be He, as we find in Midrash Konein. And through Kedushah we fulfill (Vayikra 22:33): "And I shall be sanctified in the midst of the children of Israel." And through this, holiness is conferred upon us, as the verse concludes: "I am the L-rd who sanctifies you." And through "Amen, yehei shemei rabbah" one is forgiven for all of his sins, as our sages of blessed memory have said (Shabbath 119b): "If one says 'Amen, yehei shemei rabbah' with all of his strength [i.e., with all of his intent], even if there is a trace of heresy in him, he is forgiven."