The general need of purification in the Christian congregations:
Related Commentaries of 1 Corinthians 5:6
1 Corinthians 5:6-8
6 Your glorying is not good. Know ye not that a little leaven leaveneth the whole lump?
7 Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificedb for us:
8 Therefore let us keep the feast,c not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth.