The Seder begins with kiddush, which expresses the sanctity of the Jewish people and of the Pesaĥ holiday. The kiddush of Shabbat and other holidays contains the phrase “in commemoration of the Exodus from Egypt,” for the source of Israel’s sanctity began to reveal itself with the Exodus from Egypt, when it was made known that God chose Israel to be His special nation. At the Seder, on the night we left Egypt and are commanded to tell the Exodus story, the importance of kiddush is thus compounded. It is therefore fitting to begin the Seder with it.
Thus, unlike other kiddushim where only one person recites kiddush and drinks the majority of a cup of wine, on the Seder night each participant is poured a cup of wine, and after kiddush everyone reclines and drinks most of the wine in his cup. This is the first of the four cups of wine.
The rabbinic enactment to recite kiddush over wine expresses an important principle in Judaism. People tend to think that sanctity manifests itself in the spiritual realm alone, through prayer and Torah study, assuming that the more one denies the body, the more sanctity he attains. Yet, the fact that the Sages instituted kiddush over wine teaches us that sanctity can infuse and find expression even through physical food. This is true not only of the staple foods necessary for human sustenance, but even of wine, which brings people joy. Israel’s sanctity can be revealed in its totality specifically through the fullness of life, which combines the truth of Torah and faith with happiness and joy. We therefore recite kiddush over wine.
On every Yom Tov, we recite the berakha of “she-heĥeyanu,” blessing God “Who has given us life, sustained us, and guided us to reach this season,” because Yom Tov is a mitzva that is celebrated anew during a specific season. The Sages inserted she-heĥeyanu at the end of kiddush; after declaring the day’s sanctity, it is only fitting to bless and thank God for having guided us to this sacred time. If one neglects to recite the she-heĥeyanu after kiddush, he must recite it whenever he remembers, as long as Pesaĥ has not ended.
Many people say a preliminary statement of intention (“hineni mukhan” or “le-shem yiĥud”) before each of the four cups of wine. One should not do so between the berakha and drinking, as this constitutes an interruption. Rather, the formula should be recited before kiddush, and in the case of the other three cups, before the berakha on the wine (MB 473:1).
If the first day of Pesaĥ coincides with Shabbat, we invoke Shabbat in the kiddush. If it begins on Saturday night, two berakhot are added: on the creation of fire (“borei me’orei ha-esh”) and on the separation of different forms of sanctity (“Ha-mavdil bein kodesh le-kodesh”) (SA 473:2).
. Kiddush on Shabbat is clearly a Torah precept, as it states: “Remember the Sabbath day to sanctify it.” According to Rambam and the majority of poskim, one fulfills his Torah obligation to remember Shabbat by reciting the Friday night prayers. The Sages, however, instituted that kiddush be recited over wine. According to some Rishonim, the biblical mitzva is to sanctify the Shabbat over a cup of wine.
With regard to kiddush on Yom Tov, the poskim disagree whether it is from the Torah or of rabbinic origin. Magid Mishneh on MT Laws of Shabbat 29:18 states that kiddush on Yom Tov is rabbinic, and this is also the opinion of MA 271:1 and most Aĥaronim. Conversely, many Rishonim – She’iltot, Behag, Raavya, and Maharam of Rothenburg – maintain that kiddush on Yom Tov is from the Torah, as it states: “These are the festivals of God, that you shall call holy.” See Responsa Ĥazon Ovadia §2 for a summary.