The Bnei Yissaschar (י שורד ד רמאמ) elaborates on the fact that the three Cardinal Sins upon which one must sacrifice his life rather to transgress them is hinted in the three mitzvos of Rabben Gamliel Pesach Matza and Maror. Maror corresponds to murder as מרור is gematriah מות. Korban Pesach was the avodah zarah of Mitzrayim that they worshipped before they did teshuvah. Matzah corresponds to גילוי עריות In order for dough to become chametz air רוח has to be exposed to it. There is a spiritual ruach that makes one fall prey to immoral behavior as Chazal say on a Sotah woman אין אדם חוטא אלא נכנס בו רוח שטות ak"s.
It is interesting that all three aveiros have some association with the mouth. The passuk speaks about עבירת עריות with the expression הלכא ומחתה פיה (Mishlei 30,20). It is compared to eating. By the wife of Potifar we find the lashon that Potifar put Yosef in charge of all his property except the הלחם אשר הוא אוכל meaning his wife. The only woman who had relations with a Mitzri during the galus of Yisrael in Mitzrayim was Shulamis Bas Dibri and Chazal say that she fell into that aveirah because she was too loose with her talking saying shalom to everyone.
Avodah zarah is associated with דיבור speech as Chazal say וליאכ סעוכה לכ עבד עבודה זרה The passuk says האמנתי כי אדבר that Dovid Hamelech wrote on himself I attained emunah in Hashem because I spoke about it. The passuk Devarim 13,6 ךיחא ךתיסי יכ when your brother will advise you to follow him and worship avodah zarah. It is through dibbur that one comes to avodah zara. The Baal Haturim there writes that יסיתך is referring to persuasions by food. ומכ ךשפðו כðמי באכילה ושתיה. והייðיסיתך, ההוא ו אכילה.ðפשך שבעך, דהייðכ. Chazal write on Adam Harishon that when he ate from the fruit aitz hadaas it was as if he transgressed avodah zarah.
Where did this aveirah stem from? The sefarim tell us that it was through the speech of the Nachash who gave the advice to become like Hashem if he will eat from the tree.
The aveirah of murder also comes from the mouth for Chazal tell us that if you embarrass someone it is tantamount to killing him. Also it is known that in a deep heated argument people have been killed.
So we have shown how the three Cardinal aveiros correspond to the Pesach Matzah and Maror and can all be caused by the mouth. The night of Pesach we eat mitzvah foods to rectify any wrong doing we did with these three aveiros, all the way back to Adam Harishon (see Bnei Yisasschar here). We also have to use our mouths not only to eat them with kavannah but also to praise Hashem for giving us the opportunity to rectify them.
