Why is this feast important? One reason is that it tells us something about the kind of bread Jesus was holding when he broke it and said, "This is my body." ... There would not have been a scrap of regular bread on the table or anywhere else in the house because Jews were required to eat the Passover meal using only unleavened bread. In fact, leavening of any kind was forbidden for the entire seven days of the Feast of Unleavened Bread, starting with the Passover meal. So Jesus would not have been holding ordinary bread, but matzah.
Why is this significant, and what's so terrible about yeast anyway? In ancient times leavening was done by adding a blog of old, raw, fermented dough to the new dough. The fresh batch was deliberately infected with microbes that would cause it to rise, but then later to sour, decay, and eventually rot. The puffiness of the leavening reminded the Jews of human pride and hypocrisy. Throughout the year, all grain offerings given to the Lord by fire had to be free of leaven. The ancients saw leavening as a picture of sin and contamination, something God didn't want in his burnt offerings.
So when Jesus held up the bread and said, "This is my body," on the night before his death, he was using a specific kind of bread, made without leaven, unadulterated by decay. Unlike the rest of humanity, Jesus had not been infected with the "rottenness" that was in the rest of humankind. He alone was a fit offering for our sins. When God prohibited his people centuries earlier from eating leaven during Passover, perhaps he was thinking ahead to the night when Jesus would take the bread in his own hands, break it, and then say, "This is my body, given for you."
