Remember the Shabbat day to sanctify it. (Exodus 20:8)
Our sages explain that we sanctify Shabbat by making Kiddush on Friday night (Pesachim 106a and Brachos 20b). This is considered a Torah obligation, whereas the Kiddush we recite on Shabbat day after the synagogue services is a rabbinic commandment.
There are many different customs regarding the way Kiddush on Friday night is recited. Rabbi Yosef Karo (d. 1575) rules in the Shulchan Aruch (Code of Jewish Law) that Kiddush should be recited standing (Orach Chaim 271:10) whereas others rule that while it is permissible to stand it is preferable to sit (Kol Bo).
The Chofetz Chaim (d. 1933) explained the rationale behind the two positions. Since Kiddush contains verses which testify that God is the Creator of the Universe, the person reciting Kiddush acts as a witness. Witnesses must always stand when giving testimony in a Jewish court of law. Nevertheless, the Talmud teaches that we can only make Kiddush in the place where we plan to eat our meal: Kiddush b’mekom seuda (Pesachim 101a). Since we sit at the table to eat, the Talmud implies that we should make Kiddush there as well (Mishnah Berurah 271:46).
The Vilna Gaon (d. 1797) sat for Kiddush but for a different reason. Kiddush is usually made by the head of the household for all those present, fulfilling the idea of b’rov am hadrat haMelech – the King is glorified in the multitudes. However, there must be something which confers the status of a group upon those present. This is achieved by sitting together at the table (Mishnah Berurah ibid.).
Rabbi Moshe Isserlis (d. 1572) took a novel approach. He ruled that the first paragraph of Kiddush should be said while standing (to satisfy the idea of giving testimony) after which everyone sits to satisfy the Talmudic principle of Kiddush b’mekom seuda.
The act of making Kiddush on Friday night reminds us that just as God created the Universe in six days and rested on Shabbat, so too we must build and create during our working week, but remember to reflect on our efforts and sanctify Shabbat as our oasis in time.