Kedusha Customs

What is the source for bowing left , right, then straight during kedusha?

Shalom!

Thank you for your question.

This mysterious practice is actually without any known solid origins! It is noted that there are no records of any great Rabbis in earlier generations ever doing so. Nevertheless, the practice has become somewhat mainstream and over the years a number of interpretations have been offered to rationalize it.

The siddur "Tefila L'David" of the Lelover Chassidim says that when the angels praise God with the threefold declaration of "Kadosh", they first call out to each other in order to praise Him in unison. Since the angels stand on either side of God, bowing to the right and left is intended to request permission from them to praise Him as they do.

Similarly, it is also suggested that bowing to the right and left represents the members of the congregation turning to one another in order to praise God as one, just like the angels do. This emphasizes the vital aspect of achdut, unity, during prayer – a unity characteristic of the angels. Indeed, there was once a custom, now extinct, not to bow right and left at "V'kara Zeh El Zeh V’amar," but rather to wave one's hands towards others in one's proximity. This is done even nowadays by Turkish Jews prior to the recitation of the silent Shemoneh Esrei each morning.

Some commentators explain that bowing to the right and left is intended to recall that G-d is praised from all sides by the Heavenly hosts. It is worth noting that bowing from side to side is also practiced elsewhere, such as in Birkat Kohanim, Oseh Shalom in Kaddish and the end of Shemoneh Esrei, and at Bo'i Kallah in Lecha Dodi.

There is also a theory that the liturgical song of "Amitzei Shechakim", which is recited on Yom Kippur, is the source for the custom to bow at Kedusha. The song mentions the angels turning to "every side" when reciting the Kedusha praises.

It appears from all sources that bowing at "V'kara Zeh El Zeh V'amar" is related to the angels in one way or another.

Sources from Minhag Yisrael Torah, OC 125:2.