v1: Immorality was tolerated in the church; it seems that the incident involved a man and his step-mother, but clearly the culprits were known in the church. Such immorality was an on going relationship, rather than a single misdemeanour, and the church had failed to deal with it.

Even in a society where all manner of sexual practices were pursued, the Christian has a clear responsibility to remain pure and obedient.

v2: The Corinthians were "proud" about their attitude, perhaps claiming to be forgiving and gracious. When such a serious situation arises, and the Name of the Lord is dishonoured, proper discipline is necessary. There should be grief in the church that this had happened. The guilty party must be "put out of your fellowship", see v5.

v3-4: Judgment is necessary in such circumstances. This implies something public, as the sin had been public and open. When the church gathered together, then judgment is exercised. This would be a warning to others also (1 Tim 5.20). It was also a demonstration of the unity of the church, that the standards of God were being maintained.

v5: The man discipline was solemn, as the man was handed over to Satan, see 1 Tim 1.20. To be put out of a local church in this way was something very serious. It meant the loss of great blessings.

The man who was judged would not be lost eternally, if he was genuinely converted. He would be outside the church, but remain a brother not an enemy (2 Thess 3.14-15). In other circumstances a warning was necessary (Titus 3.10); it may have been that this man had previously been warned.

v6: To tolerate such sin is to allow such sin to spread, for it appears to be condoned. It was possible that the person was quite influential in the church. The picture here is of yeast spreading through bread, and sin and sinful attitudes can do the same in a church.

Unless we deal decisively with sin it will spread. This is illustrated in Judges, where Israel failed to cast out the Canaanite peoples, who brought bad influences into the nation.

v7-8: At the time of Passover, the Jew would remove all leaven from his home, in line with the Feast of Unleavened Bread; by the first century the two Feasts were virtually one, Matt 25.17; Mark 14.1,12; Luke 22.1,7. Paul assumes that the Corinthians had some knowledge of these O.T. Feasts.

As Christians we are to remove anything which is not good, such as malice and wickedness, and be filled with truth and sincerity. Christ is our Passover, utterly without sin. In reality we are already 'unleavened', "as you really are", and we must live accordingly.

v9: Paul refers to a previous letter which he had sent to Corinth. The command, "not to associate with sexually immoral people" is consistent with the earlier commands, see v2,5.

v10: Paul addresses a possible misunderstanding. We will come into contact with the sexually immoral people of the world, such as Jesus did; their lifestyles are immoral, and we expect nothing else, for only Christ can deliver them from sin (6.11). We cannot expect unbelievers to honour God's standards, they need to be converted first. We are entitled to mix with such, to demonstrate a godly lifestyle.

v11: Paul's concern was for "anyone who calls himself a brother"; those who belong to Jesus must play by His rules! The command is that we are not to keep company, nor even to eat, with such a person. The sins noted here refer to persistent sins, as in Gal 5.21, contrast Gal 6.1, which refers to an individual caught in a single sin.

v12-13: We have no right to judge those outside; our call to them is to repentance from their sin, and to faith in Christ. God can judge them in this life (Rom 1.26-27).

The 'legal' argument continues into chapter 6.