Chapter 18 — Part II: The Sacraments — The Holy Eucharist
Section 33. The peculiar suitableness of the consecration of unleavened bread to express that integrity and purity of mind which the faithful should bring to this Sacrament we learn from these words of the Apostle: Purge out the old leaven, that you may be a new paste, as you are unleavened. For Christ our Passover is sacrificed. Therefore, let us feast, not with the old leaven, nor with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth.