Once, when the Rebbe Maharash was traveling through Berditchev, he saw a group of elderly Tolna chassidim carrying buckets of water and scrubbing the walls and floor of a little shul in preparation for a visit from their Rebbe the following day.

When the Rebbe asked them why they were doing all the work themselves instead of letting the younger chassidim help them, they answered, “We are doing this ourselves because we want to have healthy angels to assist the advocating angels who come out of the tekios, the blasts of the shofar.”

One of them explained: “You know the Yehi Ratzon that is said after the tekios of Rosh HaShanah — the one that mentions ‘the angels that are formed from the blowing of the shofar, and from the tekia, the shevarim, the teruah, and the tekiah, (kshr”k),’ [the identifying letters of the Hebrew words that signify the various sounds of the shofar]? Well, one Rosh HaShanah the holy Rav of Berditchev said: ‘Sweet Father, compassionate Father! Just in case the angels that proceed from the shofar that Levi Yitzchak the son of Sarah has just blown are weak angels, let their place be taken by the holy, healthy angels that were created by the toil of Your people in preparation for Passover, as they cleaned their kitchen utensils in order to fulfill their mitzvah as perfectly as possible: kratzen (scouring), shobben (scraping), rieben (rubbing), and kasheren (making kosher)!’” — [for the initials of these four Yiddish words are likewise kshr”k].

Likkutei Dibburim, vol. 1, p. 280