What the Bible says about Purge Out Sin
(From Forerunner Commentary)
"Clean out the old yeast," Paul says in verse 7. It is a call, in symbolic terms, to purge oneself of evil. He then takes it one further step, saying that the immoral person should be put out of the congregation. He commands this because the person's immorality contradicts everything that the church teaches, and if the person remains in the congregation, it will become spiritually contaminated and will no longer be able to consider itself as Christian. An immoral "member" is a blot on the integrity of the church.
John W. Ritenbaugh
New Covenant Priesthood (Part Two)