The Mishna teaches: “Rabban Gamliel would say: ‘Whoever does not say these three things on Pesaḥ has not fulfilled his obligation, and they are: Pesaḥ, matza, and maror‘” (Pesaḥim 126a).
This means that even one who cannot recite the entire Hagada must at least delve into the three food-related mitzvot of the Seder night. The Torah thus states regarding the mitzva to teach the child who does not know how to ask: “Tell your child on that day: ‘It is because of this that God did for me when I left Egypt’” (Shemot 13:8), and the Sages teach: “‘because of this’ means when matza and maror are before you on your table” (Mekhilta Bo 17). This teaches that one must at least reflect upon the reasons for the three foods we have been commanded to eat on the Seder night. Even though we are unable to offer the Paschal sacrifice nowadays, we are nonetheless commanded to recall its meaning.
Because, as we have seen, the Seder is conducted in question-and-answer form, we recite: “The Pesaḥ [sacrifice] that our ancestors would eat when the Temple still stood, what is it for?”; “This matza that we eat, what is it for?”; and “This maror that we eat, what is it for?”
The Paschal offering expresses Israel’s special relationship with God, matza expresses freedom, and maror expresses the significance of the enslavement.
The Paschal offering expresses Israel’s special relationship with God because it recalls God’s miraculous differentiation between Israel and other nations, slaying the Egyptian firstborn while “passing over” the homes of the Israelites. One might say that Israel’s special status is not obvious to all as long as the Temple lies in ruins, and so we cannot offer the Paschal sacrifice nowadays.
The matza, though, which expresses our redemption from Egypt, is a perpetual mitzva, as we have never lost the freedom we obtained when we left Egypt and became wholly attached to God. This is true freedom, because only one who occupies himself with Torah is truly free. Even when we are enslaved among the nations, our spirit remains free, for the Torah allows us to transcend material enslavement.
Maror is a mitzva of rabbinic origin during periods when the Paschal sacrifice cannot be offered. Maror alludes to the pain and bitterness of the enslavement, and perhaps it is only when we are able to offer the Paschal sacrifice that we can grasp the full meaning of our suffering, which refines and purifies us, and understand how our salvation sprouted from all of our travails. Then, the mitzva to eat maror becomes de-Oraita. But when the Temple is in ruins and we do not have the privilege to bring the Paschal offering, we must still believe that all our suffering is for the good. Nevertheless, it is hard for us to understand the full meaning of our suffering and see how our salvation arises directly from them. Therefore, the mitzva of maror is de-rabanan.