One deadly cancer cell can be disastrous to an entire body of healthy cells. A little leaven leaveneth the whole lump. The Church at Corinth had a member who was openly involved in immorality. The Church had not mourned over this, nor had they taken any action at all. This is the great problem in many churches today.
Sin is tolerated.
Sin is condoned. Sometimes sin is even promoted in the Church. Preachers, deacons, and prominent members are commonly reported to be guilty of fornication and adultery, and nothing is done about it. The Bible standards for the ministry and church officers are ignored in many quarters today. No wonder the world has lost all respect for the Church.