Yechiel Michel Epstein

“ Section 4 One can also point out that in truth Shabbos depends on Pesach and Pesach depends on Shabbos, for Shabbos testifies to G-d's creation of the world, and Pesach testifies to G-d's divine providence over and love for the Jewish People. One without the other would not suffice, as is understood [in religious philosophy] . Therefore immediately after the Exodus from Egypt the Holy One Blessed be He gave us the commandment of Shabbos, and He did not wait until the giving of the Torah. This is because Pesach requires the ideology of Shabbos, and Shabbos requires the ideology of Pesach. ”

“ Some write additionally that if the eve of Pesach should fall on a Shabbos these public discourses should take place on the previous Shabbos (Chok Yaakov) . This point of view works well for those who understand that the discourses are on the laws of Pesach. In our communities, where everyone asks their specific questions from their Rabbi, and the public discourses are given over to other religious matters, there is no reason not to hold them on Pesach eve [if the calendar falls out so] . ”

“ This is the meaning of the verse "To strike the Egyptians through their firstborn, as is explained in the Midrash. It is due to this miracle [that the Egyptians entered into internal strife instead of attacking the Israelites] that gave rise to this Shabbos being called the 'Great Shabbos'.
Section 2 Now if you should ask: 'What does the Shabbos have to do with this? let the commemoration always be on the tenth of the month' - know that there is an answer, which is that the tenth is also the anniversary of Miriam's [Moshe's sister] death, and therefore was not chosen to be a day of rejoicing. ”