Matzah and Bitter Herbs
Rabbi Bunam said: "We eat the Seder meal in the following order: the matzah first and the bitter herb next, though it woul seem the reverse order is proper, since we first suffered and later were freed. The reason for this, however, is that as long as there was no prospect of being redeemed, the Israelites did not feel keenly the bitterness of their lot. But as soon as Moshe spoke to them of freedom, they awoke to the bitterness of their slavery."
Source: Siach Sarfei Kodesh
