The gospel of Jesus Christ is unique. All other moral belief systems expect that good people should be rewarded and bad people excluded: the difference between them is determined by their piety, personal discipline and devotion to religious rites. But the gospel proclaims that dirty people can be washed clean; those who have lived unholy lives can be sanctified.
 
That does not mean that sinful behaviour does not matter, or that God will indefinitely tolerate wickedness (Luke 13:5-9). Paul is clear that people who persist in disobeying the Lord have no place in His home: if they cannot be trusted to run their own lives in the light of heaven, then they cannot expect to go there (Luke 16:10). Even though the culture of Corinth, which had invaded the church, was noted for its sexual licence and shady business practices, it was not the culture of God's kingdom and would not be accepted there.
 
However, the Corinthian church was made up of people from that immoral society: 'that is what some of you were …' (1 Corinthians 5:10-11). Their lifestyle had been offensive to God - but when they repented and received Christ, their hearts were changed. His blood had washed away their sin and His Spirit had enabled them to hate what they had loved, and love what they had once despised. The wonder of the gospel is that instead of being far away from God's kingdom, they had been brought near to the holy God who made them and loved them.
 
Paul's message still applies to a world where evil is acceptable and righteousness is despised, especially where that has been tolerated in the church. Nobody is too bad for God's grace to reach and heal him or her; and all who repent must learn to live a transformed life. The blood of Jesus Christ atones for their sin, and the indwelling Holy Spirit empowers radical lifestyle change (Titus 3:5). That is why the Lord received sinners (and still does), but taught them how to change and gave them His Spirit to enable them to live differently and tell others (Acts 1:8). That is an amazing gospel to share with your friends and colleagues (www.crosscheck.org.uk); introduce somebody to Jesus who welcomes sinners and changes those who repent. And we in His church must learn to live it too (Ephesians 5:3-6).