Hacham Ovadia Yosef, in his work Halichot Olam (Parashat Vayera), discusses a number of laws and customs relevant to the recitation of the phrase "Bo’i Kalla" (literally, "Come, O bride!") during the Kabbalat Shabbat service (listen to audio recording for precise citation). We recite this phrase toward the end of the "Lecha Dodi" hymn, and one should recite the words "Bo’i Kalla" three times. Hacham Ovadia writes that one should recite this phrase the first time while bowing slightly to the left, and the second time while bowing slightly to the right. While reciting "Bo’i Kalla" for the third time, Hacham Ovadia writes, one should bow slightly straight in front of him. This series of bowing resembles the bowing which we do while reciting "Ose Shalom" at the end of the Amida – first to the left, then to the right, and then to the center.
Hacham Ovadia argues in this regard with the Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), who held that one should not bow while reciting "Bo’i Kalla." Instead, according to the Ben Ish Hai, one turns toward the right while reciting "Bo’i Kalla" for the first time, then to the left the second time, and to the center for the third and final recitation. Hacham Ovadia, however, follows the view of Rav Haim Palachi (Turkey, 1788-1869), that one should slightly bow, first to the left, then to the right, and then to the center.
Hacham Ovadia also discusses in this context the proper intention that one should have while during this recitation. He writes that when reciting "Bo’i Kalla," one should think in his mind that he accepts the "Nefesh," the first aspect of the "Neshama Yetera" ("additional soul") which we receive on Shabbat. We accept the second level of this additional soul, the "Ru’ah," when we answer to Barechu at the beginning of Arbit. Finally, we accept the third level, "Neshama," just before the Amida at Arbit, when we recite, "U’fros Alenu…" One should stand at all three of these points, as he accepts the different levels of the "Neshama Yetera."
The prevalent custom is to turn facing the western side of the synagogue when reciting "Bo’i Kalla" to greet the Shabbat. Of course, when we turn to face the western side of the synagogue, our backs are turned to the east side, where the Hechal (ark) is situated. Although Halacha generally forbids turning one’s back to the Hechal, Hacham Ovadia writes in a responsum (Yehave Da’at 3:19) that this is permissible for the purpose of giving honor to the Shabbat by turning to the western side. Furthermore, he notes, the Torah scrolls are closed in the ark which is covered by a Parochet (curtain), and is also above ten handbreadths from the ground, such that we are not actually turning our backs to the Torah.
The Ben Ish Hai writes that when one recites "Bo’i Kalla" the first two times, he should do so in a loud voice, whereas the third recitation of "Bo’i Kalla" should be done in a low, quiet voice.
Summary: At the end of the "Lecha Dodi" hymn in the Friday night Kabbalat Shabbat service, we recite the phrase "Bo’i Kalla" three times – twice in a loud voice, and the third time in a low voice. Each time one recites these words, he should bow his head slightly – the first time to the left, then to the right, and then to the center. One should have in mind during this recitation to receive the first level of the "extra soul" which is bestowed upon us on Shabbat. "Bo’i Kalla" should be recited while one is turned facing the western side of the synagogue.
