Thematic Bible: A symbol for sin

Your rejoicing is not good. Do you not know that a little leaven leavens the whole mass? Remove the old leaven, that you may be a new mass, as you are unleavened; for Christ our passover was also sacrificed for us. Let us therefore keep the feast, not with old leaven, nor with a leaven of vice and wickedness, but with the unleavened bread of sincerity and truth.