Allowing sin to enter and stay in your lives is not a good thing. In 1 Corinthians 5:6 Paul says, Your boasting is not good. Don’t you know that a little yeast works through the whole batch of dough? A little bit of yeast in a batch of dough goes a long way, just as a little bit of sin in our lives tends to work its way into more sin. While the expectation is not that we need to be sinless, we are supposed to fight deliberate sin in our lives.