Leavened vs. Unleavened Bread in the Eucharist

1 Cor 5:6-8

Your boasting is not appropriate. Do you not know that a little yeast leavens all the dough? Clear out the old yeast, so that you may become a fresh batch of dough, inasmuch as you are unleavened. For our paschal lamb, Christ, has been sacrificed. Therefore let us celebrate the feast, not with the old yeast, the yeast of malice and wickedness, but with the unleavened bread of sincerity and truth.

Catechism

#1334

In the Old Covenant bread and wine were offered in sacrifice among the first fruits of the earth as a sign of grateful acknowledgment to the Creator. But they also received a new significance in the context of the Exodus: the unleavened bread that Israel eats every year at Passover commemorates the haste of the departure that liberated them from Egypt; the remembrance of the manna in the desert will always recall to Israel that it lives by the bread of the Word of God;156 their daily bread is the fruit of the promised land, the pledge of God's faithfulness to his promises. The "cup of blessing"157 at the end of the Jewish Passover meal adds to the festive joy of wine an eschatological dimension: the messianic expectation of the rebuilding of Jerusalem. When Jesus instituted the Eucharist, he gave a new and definitive meaning to the blessing of the bread and the cup.

#1339

Jesus chose the time of Passover to fulfill what he had announced at Capernaum: giving his disciples his Body and his Blood:

Then came the day of Unleavened Bread, on which the passover lamb had to be sacrificed. So Jesus sent Peter and John, saying, "Go and prepare the passover meal for us, that we may eat it. . . ." They went . . . and prepared the passover. And when the hour came, he sat at table, and the apostles with him. And he said to them, "I have earnestly desired to eat this passover with you before I suffer; for I tell you I shall not eat it again until it is fulfilled in the kingdom of God.". . . . And he took bread, and when he had given thanks he broke it and gave it to them, saying, "This is my body which is given for you. Do this in remembrance of me." And likewise the cup after supper, saying, "This cup which is poured out for you is the New Covenant in my blood."166

#1340

By celebrating the Last Supper with his apostles in the course of the Passover meal, Jesus gave the Jewish Passover its definitive meaning. Jesus' passing over to his father by his death and Resurrection, the new Passover, is anticipated in the Supper and celebrated in the Eucharist, which fulfills the Jewish Passover and anticipates the final Passover of the Church in the glory of the kingdom.