1 Corinthians 5 v 6


1 Corinthians 5:6
Your glorying is not good. Know ye not that a little leaven leaveneth the whole lump?


5:6. There was, of course, no excuse for the Corinthians’ pathetic behavior. Paul reminded them of a truth they already knew but were failing to practice—a little yeast soon permeates the whole batch of dough. A small sickness can eventually kill a body. The need for church discipline is based on the same principle.

Excerpt from:
Walvoord, J. F., Zuck, R. B., & Dallas Theological Seminary. (1983-c1985). 
The Bible knowledge commentary : An Exposition of the Scriptures. 
Wheaton, IL: Victor Books.