Question: Should one stand or sit when making kiddush on Friday night?
Answer: The Rambam (Shabbos 29:1) says there is a mitzvah d’Oraisa to sanctify Shabbos with a verbal statement. Later (Shabbos 29:6), he says the Sages instituted that the verbal statement be said over wine.
There are four customs regarding whether one should sit or stand by Kiddush at night. I'll bring them and some of the reasons behind them. One should follow their family’s custom.
The Beis Yosef (271:10) brings from the Kol Bo (41) that although one should stand by Kiddush in honor of the King (Hashem), we don’t stand but rather sit because we need Kiddush b’makom seudah, Kiddush in the place of the meal. The Kol Bo assumes that although we should stand, standing even at the table would take away Kiddush b’makom seudah, so we sit.
The Shulchan Aruch (271:10) rules that one should stand for Vayechulu. The Mishnah Berurah (271:45) and Kaf HaChaim (271:61) explain this is because Vayechulu is a testimony, and testimony needs to be said while standing. The Beis Yosef says there is no problem of Kiddush b’makom seudah since standing very close to the table is still considered Kiddush b’makom seudah.
The Rama says it’s better to sit by Kiddush, even for Vayechulu. The Mishnah Berurah explains that since we already said Vayechulu in shul, we don’t need to repeat it while standing. However, the custom is to stand for the first four words (Yom HaShishi Vayechulu HaShamayim) because the first letters of these four words spell Hashem’s name, and this is done out of respect for Hashem’s name.
Igros Moshe (O.C. 5:16:5), says one should stand for the entire Vayechulu and then sit down, because many times someone at the meal was not in shul. Even if everyone at the meal was in shul, to maintain uniformity and avoid confusion, we always stand for Vayechulu.
The Mishnah Berurah (271:46) brings another reason to sit from the Gra, which is that sitting creates a more established setting. One can only fulfill his obligation through someone else when the one reciting Kiddush is in an established setting. The Mishnah Berurah understands from the Gra that even those listening should preferably sit, not just the one making Kiddush. Ma’aseh Rav (121) says the Vilna Gaon would sit for Kiddush.
The Kaf HaChaim (271:62) brings a fourth custom from the Arizal that one should stand for the entire Kiddush. Later (271:64), he says that one should sit down when drinking the wine after Kiddush because a Torah scholar doesn’t drink while standing. The Elya Rabba (296:14) adds that even if one is not a Torah scholar, they should still sit while drinking.
The Mishnah Berurah (271:46) emphasizes that those who stand should do so in one area rather than spreading out all across the room.
In short, there is a biblical mitzvah to sanctify Shabbos. The Sages instituted that it be said over wine. There are four customs regarding standing by Kiddush: 1. Stand for the entire Kiddush. 2. Stand for Vayechulu. 3. Stand for the first four words of Kiddush. 4. Sit for the entire Kiddush.
One should follow their family’s custom.