At Kadesh – we drink the first of the four cups of wine. Each cup symbolises a particular highlights of the seder: the first at Kadesh, the second at Maggid, the third at Barech and the fourth at Hallel.
The function of a kiddush is twofold.
Firstly, to distinguish between that evening and other evenings. The word itself means “to separate”. The way we do this is through remembering the Exodus – זכר ליציאת מצרים – in memory of the departure from Egypt. The reason we do this is because this is the very foundation of being Hashem’s people.
Secondly, the function of a kiddush is to express service and allegiance to Hashem. This is true of kiddush on every Shabbos and all Yomim Tovim. This is the first cup of wine that we drink.
The second is drunk after Maggid. Maggid’s place in the Seder is to perform the mitzva – exclusive to Seder night – of in depth discussion of the events of redemption from Egypt – סיפור rather than the זכר of Kadesh. The function of the mitzva of סיפור יציאת מצרים is to recreate and relive the events, rather than to remember. The wording of the halacha is “כל דור ודור חייב אדם לראות את עצמו כאלו הוא יצא עתה” – a reliving.
To fulfill the mitzva of סיפור , there are three requirements. The first is the most basic – the educational engagement that occurs in question and answer form. It is dialogue that differentiates it from the monologue of a זכר.
The second requirement of סיפור is for the participants at the Seder to imagine Yetzias Mitzrayim. This is achieved through story telling. As with any story, it begins with a problem and ends with a solution.
The final, most demanding requirement of סיפור is the טעמי הצמוות – the rationale behind the mitzvos of the Seder must be explained and understood.
R’ Chaim Brisker says that these requirements distinguish the mitzva of סיפור from the regular mitzva of זכר . The mitzva of סיפור constitutes a key highlight of the Seder, and this is why the second cup of wine is drunk at the end of Maggid.
The third cup is consumed at the conclusion of Birchas Hamazon, Barech. The blessing gives thanks to Hashem for what we have eaten – including the Matza and Maror, as well as the meal. The Birchas Hamazon is the conclusion of all the mitzvos of the evening, and as such, the reason we drink the third cup of wine at this point.
The fourth cup is drunk at the conclusion of Hallel. Hallel is a shira, a song of praise and gratitude for all the kindness Hashem has done for us, which is what the entire Seder was about.
Wine is prestigious and indicates prominence – the reason it is used for any kiddush. We mark the prominent events of the Seder, at which point we drink, encompassing the entire evening.