Bnei Yissaschar, Nisan 5:13/בני יששכר·ניסן ה׳:י״ג

1Blessed is the Holy One, Blessed is the One who gave us Torah. One should ponder on the relevance here of giving the Torah. It appears to me, however, that the letters of the Torah were also in exile in Egypt. And it was on account of the iron furnace that the exiles were able to leave their exile and come to the time of the giving of the Torah. This is what is meant by (Exodus 3:12) "And this shall be the sign (ot)" - meaning the letters (otiot) of the Torah. Now the 27 letters of the Torah are pure, (zach), and each of them consists of all of them. 27 multiplied by 27 is equal to "Pesach, Matzah and Maror." Therefore these are the three things that Rabban Gamliel obligated us to declare on Pesach, in order to show the greatness of using the mouth to express the letters of the Torah which we are commanded to speak.