In 1 Corinthians 5 we learn that unrepentant sin is something that permeates and infects the entire church. Just as a little leaven causes the entire lump to rise so too does unrepentant sin spread and lead others to go down the same sinful path. That's how serious sin is. That's why Paul calls for the church at Corinth to cleanse out the leaven of malice and evil and be unleavened.
1 Corinthians 5 | Cleanse out the Leaven of Malice and Evil | Pastor Mike Hyatt | 29:04