פירוש על פסחים 10:5

כל שלא אמר ג' דברים אלו – that he did not explain the reasons of these three things.

Rabban Gamaliel used to say: whoever does not make mention of these three things on Pesah does not fulfill his duty. And these are they: the pesah, matzah, and bitter herbs. The pesah because the Omnipresent passed over the houses of our fathers in Egypt. The matzah because our fathers were redeemed from Egypt. The bitter herb because the Egyptians embittered the lives of our fathers in Egypt. In every generation a man is obligated to regard himself as though he personally had gone forth from Egypt, because it is said, “And you shall tell your son on that day, saying: ‘It is because of that which the Lord did for me when I came forth out of Egypt” (Exodus 13:8). Therefore it is our duty to thank, praise, laud, glorify, raise up, beautify, bless, extol, and adore Him who made all these miracles for our fathers and ourselves; He brought us forth from slavery into freedom, from sorrow into joy, from mourning into festivity, from darkness into great light, and from servitude into redemption. Let us say before him, Hallelujah!
This mishnah has become a liturgical text, that is a text that is recited on a ritual occasion, namely the seder. It has been a part of the Haggadah since the Haggadah was composed. As is common, as the liturgy expanded the text of the mishnah grew as well. Below, the pieces that are in small font are later additions to the mishnah, additions which appear in our Haggadot but were not originally part of the Mishnah itself. There are other additions in the Haggadah which do not appear even in later versions of the mishnah.
Now to the content. In this mishnah Rabban Gamaliel demands that we explain the three main food items at the table, pesah, matzah and marror, while these items lay in front of us. Because he mentions the pesah, some scholars posited that this Rabban Gamaliel lived while the Temple still stood and the pesah was sacrificed. I believe it is more likely that the mishnah is representing a post-Temple reality and that this is the same Rabban Gamaliel whom we already encountered who believes that the pesah can still be eaten even without a Temple. The ritual here replaces, at least as best as is possible, the loss of the Temple. When sacrifices can no longer be offered, words, study and prayer take their place.
An interesting side note to be made is the comparison of Rabban Gamaliel with Jesus’s words at the Last Supper, assumed by three of the four Gospels to have taken place on the eve of Pesah. Jesus gives symbolic meaning to the wine (his blood) and to the matzah (his body). There is some correlation between that which Rabban Gamaliel demands and that which Jesus does according to the Gospels. Scholars have attempted to discover which ritual was earlier did the early Christians modify an ancient Jewish custom? Or did rabbinic Jews engage in polemics against Christians, saying this is the symbolic meaning and not what you say it is? I don’t believe we can know the answer to this question, and it may not be a good question. What the two faiths have in common is that both impart symbolic meaning to the seder meal in a world in which the central structure, the Temple, has been destroyed.
The mishnah itself is straightforward and probably familiar to most of us; hence I have refrained from making any direct comments.