The word immorality in 5:1 is -porneia- from -porne- a prostitute (1 Corinthian 5:1). But this is not ordinary -porneia- rather a case of unlawful sexual intercourse which isn't approved even among the Greeks (5:1), who were notorious for every other kind of sexual deviation. What is unlawful is incest with one's father's wife, which merited the death penalty among Jews (see Leviticus 20:11).
What did Paul mean by handing someone over to Satan? I assume this was not consigning the man to eternal damnation. That would be a denial of 5:5. The two most common explanatory models I have encountered are :
(a) There was some kind of exclusion from the community or being excommunicated from sharing in the bread and wine of communion. This has been used for centuries by both Protestants and Roman Catholics to excommunicate people right and left. I explain why I reject that in the chapter on Fellowship in Go Make Learners.
b) In Paul's day there was some way of allowing Satan to harm a person's body, as in the case of Job. This might explain the solemn gathering with Paul's Spirit present to do this (5:4). But it would be black magic, and it does not make clear how it would result in the man's salvation.
(c) The model that I use is that the man must be handed over to the Corinthian magistrates for punishment. Handing over to a civil court means going before pagan magistrates (6:1) In that case Paul says that petty grievances between members of the community should be dealt with within the community, not by going to a civil court (6:2-6).
The difference in 5:1-5 is that incest with his father's wife was not only punishable by the death penalty among Jews (if they acted as judges), but it was also a criminal punished very severely by Roman law. That would explain why it was behaviour which was illegal even among the Romans and Greeks (5:1).
In St. George's Cathedral in my city of Kingston we had such a case
five years ago. An organist, who had abused many of his choristers, had
to be handed over to be tried in a criminal court, and sent to jail. While
he was being tried, and even after he was jailed, we still visited and
gave him communion. I believe that excommunication in the sense of withholding
communion from the ignorant, bad people, and criminals is never right.
They need communion, as we do, most of all. But the Cathedral congregation,
many of whom hated to have the police in, were told it was necessary that
the man be taken out from among them (5:2). In that case it was
both for the protection of the choristers, and a necessary means of bringing
the man to his senses that his spirit might be saved. He went to jail for
several years, and I believe came to a deep faith.
Paul adds "in the Day of the Lord" (5:5). In the case of the Cathedral here in Kingston the terrible Day of the Lord was the trauma of an incredibly brilliant musician having his career destroyed. He will never be a great church musician again, but I think he has grown as a Christian. The problem is that in such situations other church members are kind hearted, and shrink from decisive action (5:2). Paul felt he had to be tough with the situation in his day, and let justice take its proper course. We have to be equally tough minded in our day.
What then is the meaning of handing over such a person to Satan (5:5)? In Ephesians 2:1 we are described as having been transferred into the kingdom of grace from living according to the ruler of the power of the air, obviously Satan (Ephesians 2:5). So by having the man arrested, he is handed to the sphere of law and just deserts. But in the Church we are loved regardless.
The advantage of this model is that can be expanded to two difficult verses in Matthew's Gospel. If we are angry with a brother or sister (Matt.5:22), better be reconciled, or you will both end up in a civil court, one of you will go to jail, and both will be paying legal fees to the last penny (Matt. 5:25-26). In a quarrel between Christians (Matt. 18:15-17), the matter should be settled privately, with two or three witnesses, or by their -ekklesia- church. It is only, if all else fails, that the offender should be treated as a person of the world outside. We therefore have the same model of the church as the Kingdom in which we are loved, accepted regardless, and treated as under grace. And the world outside is where people are sued, and judged, and excluded.
Here in Canada there is much discussion of the terrible situations in
which boys have been abused in residential schools. Abusing little boys
and young men is a serious crime in Canada. It was not a criminal act in
the Greek world of Paul's day, and obviously one cannot hand someone over
to justice if there is no criminal law against that act. Presumably what
we have to do is to hand criminals over to be tried by the courts in our
country. This means reporting the case to the police. But for all other
failures, character faults, and imperfections we welcome all manner of
sinners to communion with us (even when they are in jail), and trust the
Holy Spirit to change them in his own way in due course.