Question:

I regularly attend Friday night services. When we sing the beautiful song, "Lecha Dodi," everyone turns around for the last verse. My 10 year old son asked me why, but I didn't have an answer.

Answer:

We turn around for the verse in which we welcome the Sabbath Queen, ending with the words, "Come O Bride, come O Bride, come O Bride O Sabbath Queen." As we welcome the Sabbath, we turn to greet her as we would any special guest. This is a throwback to the time when people would actually go outside greet the Sabbath Queen exclaiming, "Come O Bride, come O Bride!" The holy Arizal taught his students—the mystics of the city of Tzefat—that when greeting Shabbat in the field, they should face the setting sun with closed eyes and serenade the Shabbat bride.

One of the early Chassidic masters explains that on Sabbath even the souls who are being punished, and are "pushed out," are welcomed in for a respite. When we turn around, we welcome them to their Shabbat rest.

Sources:
Talmud, Shabbat, 119a; Code of Jewish Law, O.C. 262; Shaar Hakavanot, Derushay Kabalat Shabbat, 1; Tiferet Shelomo, Metzorah.