Regarding the obligation of the reason for the cups, it is stated in the Gemara (Pesachim 108a): "Regarding wine, it was stated in the name of Rav Nachman: the reason is necessary, and it was stated in the name of Rav Nachman: the reason is not necessary. And they do not disagree, this one speaks about the first two cups, and that one speaks about the last two cups. They said to this side, and they said to that side. They said to this side, the first two cups require the reason, as now we are beginning the freedom, the last two cups do not require the reason, whatever will be, will be. And they said to that side, on the contrary, the last two cups require the reason, as that is the time of freedom, the first two cups do not require the reason, because they are saying 'we were slaves.' Now that it was said this way and that way, both require the reason."