Revealing Hashem

Through eating the portion of matzah during the Seder night, we reveal the essence of HaShem; a level uncontainable, which even the highest levels of spirituality cannot hold or fully grasp. This is hinted to by that fact that the roof was broken when the Jewish people ate the matzah.

Through such a revelation, it causes that the Hallel should be recited with a great joy and ecstasy, one that is higher than all limitations.

(Sha-arei HaMoadim, Pesach Page 113)