His words relate to Passover, whose matzah is a biblical commandment, as is the matzah itself, as written in the book of holiday customs (Chatam Sofer, Erukh Shinay Kzaytim L'Afikomen): "Matzah is the only biblical commandment of eating nowadays that is practiced from year to year." There is an obligation to eat the first olive size in the sukkah, which is a rabbinic law regarding dwelling in the sukkah, not a law of eating matzah. Although the commandment of maror is biblical only when eaten with the Passover sacrifice, we have already explained that Rabban Gamliel's words primarily refer to the time when the Temple existed. Eating matzah on the Seder night is a biblical commandment even now, as the Gra (in the Haggadah) explained according to the Rambam's opinion, that there is a commandment of matzah practiced with the eating of the Passover sacrifice, which is a condition in eating the sacrifice like the law of roasting over fire. There is also the commandment "In the evening, you shall eat matzot" (Exodus 12:18), which is a standalone commandment practiced biblically even today.