1 Corinthians 5:1 It is reported commonly that there is fornication among you, and such fornication as is not so much as named among the Gentiles, that one should have his father’s wife.
One of the Corinthian brethren was having a sexual relationship with his father’s wife – we may assume this means his stepmother.
1 Corinthians 5:2 And ye are puffed up, and have not rather mourned, that he that hath done this deed might be taken away from among you.
The Corinthian congregation were still fellowshipping this individual.
1 Corinthians 5:3 For I verily, as absent in body, but present in spirit, have judged already, as though I were present, concerning him that hath so done this deed,
Paul has made a judgment in absentia that this ought not to be allowed to continue.
1 Corinthians 5:4 In the name of our Lord Jesus Christ, when ye are gathered together, and my spirit, with the power of our Lord Jesus Christ,
Paul had power by virtue of the Holy Spirit to assist them in making a collective judgment on the man.
1 Corinthians 5:5 To deliver such an one unto Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.
To deliver such an one unto Satan. – This only makes sense if we understand that Satan is not a fallen angel. Paul is not in the business of collusion with a fallen angel. Delivering into the custody of a fallen angel is not going to effect a reformation of character – rather the contrary.
Satan, in the New Testament, is a metaphor for the lust within men that causes them to sin. Lust is the prince of this world because it rules the actions of those without God in the world.
To deliver unto Satan is a euphemism for excommunication from the body of believers – to put them back into a Godless world without the hope of salvation.
Paul uses the same phrase concerning Hymenaeus and Alexander:
1 Timothy 1:20 Of whom is Hymenaeus and Alexander; whom I have delivered unto Satan, that they may learn not to blaspheme.
For the destruction of the flesh – Paul means the destruction of works of the flesh – the lust which was ruling the man’s life. To reform, the man had to cease to live by his lust.
That the spirit may be saved in the day of the Lord Jesus – In Christ, we must be born again of the spirit. This means that we must allow the scriptures to change the way that we think and consequently behave.
Romans 12:2 And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God.
Ephesians 4:23 And be renewed in the spirit of your mind;
1 Peter 1:23 Being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth for ever.
The purpose of excommunication is to cause the man to change his way of thinking - to repent and do that which is right in the sight of God. If the man repents, his spirit – his way of thinking - will be acceptable when Christ returns to raise and judge the saints.
Luke 23:46 And when Jesus had cried with a loud voice, he said, Father, into thy hands I commend my spirit: and having said thus, he gave up the ghost (expired).
Acts 7:59 And they stoned Stephen, calling upon God, and saying, Lord Jesus, receive my spirit.
The excommunication had the desired effect. The man did repent, and Paul in his second letter exhorts the congregation to receive him back into fellowship.
2 Corinthians 2:6-10 Sufficient to such a man is this punishment, which was inflicted of many. 7 So that contrariwise ye ought rather to forgive him, and comfort him, lest perhaps such a one should be swallowed up with overmuch sorrow. 8 Wherefore I beseech you that ye would confirm your love toward him. 9 For to this end also did I write, that I might know the proof of you, whether ye be obedient in all things. 10 To whom ye forgive any thing, I forgive also: for if I forgave any thing, to whom I forgave it, for your sakes forgave I it in the person of Christ;
I hope you find this helpful.