1 Corinthians 5:6 Your glorying is not good. Do you not know that a little leaven leavens the whole lump?
1 Corinthians 5:7 Therefore purge out the old leaven, that you may be a new lump, since you truly are unleavened. For indeed Christ, our Passover, was sacrificed for us.
We are obligated then to do what we find in the next verse:
1 Corinthians 5:8 Therefore let us keep the feast, not with old leaven, nor with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth.