A Good Feast

Itaque festa celebremus, non in fermento veteri... Hoc est laetitiam habentes renovationis, facta vetera fugiamus, immunditiam omnem abjicientes a nobis, quae est corruptio; quia sicut fermentum totam massam corrumpit, ita et mala vita totum hominem. Ergo ut non solum a turpitudine vitae nos observemus, sed et ab iniquitatis studio, adjecit: Nec in fermento malitiae et nequitiae, sed in azymis sinceritatis et veritatis. Hoc est, ut sinceritas mundam vitam faciat, veritas autem omnem fraudem excludat. Ambrosiaster, In Epistolam Beati Pauli Ad Corinthios Primam, Caput V Source: Migne PL 17.209d-210a

Therefore let us not feast with the old leaven... 1 That is, possessing the joy of renewal let us be done with old deeds, and cast away every uncleanliness, which is corruption, because as leaven corrupts the whole loaf, so even a wicked life corrupts the whole man. Therefore that we should not only guard ourselves from any vileness of life, but also be careful of any iniquity, He adds, Nor with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth. That is, let honesty make life clean and let truth expel every deceit. Ambrosiaster, Commentary On The First Letter of Saint Paul To The Corinthians, Chapter 9 1 1 Cor 5.8