Paul has a kind of zero-tolerance policy for divisions in the church, the issue covered in the first four chapters 1 Corinthians. In chapters 5-6 he deals with a series of related issues which cannot be tolerated. Sexual immorality may have been part of civic banquets at temples, gluttony and drunkenness lead to lawsuits harsh words, etc.
The main problem, however is the same as the divisions within the church. The Corinthians are still thinking like pagan Romans, not like Christians. Garland points out the connection between arrogance at the end of chapter 4 and the “puffed up” in 5:2. Paul wonders how the church can consider itself as spiritual if they tolerate this kind of sin in their congregation.
In 1 Corinthians 5, Paul affirms a similar zero-tolerance policy on immorality in the church. For Paul, there is no reason for a person who is openly committing immorality to continue to fellowship with the believers in Corinth. More than this, the church continues to boast about their own spirituality even though the immoral man is a part of their church.
This case of immorality in the church is a very serious: Paul invokes the authority of Jesus Christ (both the name and power) as well as his own authority (twice), and he describes the sin as like leaven, growing throughout the entire loaf. The danger is so great, Paul commands the Corinthians six times in this one chapter to expel the sinful man from their church!
The sin celebrated by the Corinthian church was shocking (5: 1-2). This behavior is a sexual sin and is a punishable offense by Roman law. But as Bruce Winter points out Roman laws were not administered with impartiality. Those who were rich and powerful were able to avoid penalty. This is an on-going affair that is known to both the church and the community of Corinth. It does not appear from the grammar that the father is dead, nor that the father or the step-mother are Christians. Paul’s concern is only with the young man, who is presumably a Christian.
The Romans would have ignored at an older woman having an extra-marital affair with a younger man. Despite it being against the law, in some circles it was expected and a husband pressed charges against his wife would be considered strange. But a relationship with one’s stepmother was illegal in both Roman law and Judaism (Lev 18:7-8, 20:11; Deut 22:30). In the Mishnah, there is a list several categories of sexual offense that merit stoning: He who has sexual relations with (1) his mother, (2) with the wife of his father, (3) with his daughter-in-law, (4) with a male, and (5) with a cow; and the woman who brings an ox on top of herself.
The Institutes of Gaius date to the mid second century, about 100 years after Paul writes. In 1.63 Gaius states “Moreover, I cannot marry my former mother-in-law or daughter-in-law, or my step-daughter or step-mother. We make use of the word ‘former,’ because if the marriage by which affinity of this kind was established is still in existence, there is another reason why I cannot marry her, for a woman cannot marry two men, nor can a man have two wives.” The particular combination of things in this situation was an adultery and incest, there would likely have been no mercy under the law, both the man and woman would have faced exiled and forfeit of all property.
Paul’s zero-tolerance policy for immorality is an important principle for modern church discipline, although in modern American context most people who are caught in a sin like this will simply move on to another church before it comes to the point of expulsion. Paul’s concern is the on-going health of the church, a sin like this will have a grave effect on the spiritual life of a congregation. There is simply no room for toleration in this case!