I may have thought that from Rosh Chodesh [that one would have to discuss the Exodus. However,] we learn [otherwise, since] it is stated, "on that day." If it is [written] "on that day," it could be from while it is still day [before the night of the fifteenth of Nisan. However] we learn [otherwise, since] it is stated, "for the sake of this." I would only say 'for the sake of this' when [this] Matzah and Maror are resting in front of you [meaning, on the night of the fifteenth].