To be more clear, how can the person be saved in the day of the Lord Jesus Christ by delivering such person (sexual immoral) to Satan for the destruction of the flesh?
1 Corinthians 5:5 (NKJV)
5 deliver such a one to Satan for the destruction of the flesh, that his spirit may be saved in the day of the Lord Jesus.
If you read the general context of this passage in Corinthians you will find that there is a lot of stuff about church order, roles in the church, how to deal with problems inside and outside the body of believers, etc.
The verse you quote in particular starts to make sense when you see it as a reference to church discipline and understand the purpose of discipline. In this case we're specifically talking about the last possible stage of disipline: excommunication. This is the final step a church will take in trying to bring somebody who claims to be a believer into alignment with their confession. Although the step is a drastic one, the purpose is no different than the earlier steps: Christ receiving glory as people are saved and brought from darkness to light.
Excommunication (or total removal of a person from the church) serves two purposes.
It protects the church. The church is supposed to be holy: the bride of Christ spotless and reserved for Him. Of course the church is also comprised of sinners, but we are in the process of being made holy. Step by step we are supposed to be conforming to his standards and looking more like him. If somebody is moving the oposite direction — deliberately and intentionally sinning and justifying their sin, then removing them from the body prevents the corruption from spreading.
It stands as a severe warning. The hope is that by being rejected by the church they will be made aware of the seriousness of their sin before God and realize that they need to repent. Removal from the church only happens after teaching, warning, and internal discipline measures have failed — in other words the person is not listening to lighter warnings. They still insist they are Christian but also insist on living in a manner inconsistent with Christianity. By rejecting their claim to "be Christian" and not allowing them to participate in church functions, they are forced to consider whether they really are Christian.
Back to your verse in particular: "Deliver this man to Satan" is a reference to excommunication -- where the church rejects a person's claim to be Christian and forces them to live outside the community of the church. If the person truly has been chosen and is being saved by the Lord, finding themselves outside the blessing of the church gives them an opportunity to discover 1) how they are living "according to the flesh"; 2) how they need to repent; and 3) how they need to rededicate themselves to the Christian values they once espoused.
If they do these things, the church must then welcome them back into the fellowship of the local assembly, and the whole process will have benefited them and will have brought them one step closer to their complete salvation. If they do not do these thing, the process will prove they never did belong to Christ and may in fact serve another master!
A church can turn a blind eye to serious sin, allowing people who profess to be followers of Christ to live like followers of the devil with complete impunity, but that is not what Jesus had in mind for his true followers.
Excommunication, on the other hand, is a means by which a local church upholds biblical and righteous standards, punishes those who persist in unbiblical and unrighteous living, and moves one step closer to fulfilling Christ's purpose for his bride the church:
That he might present it to himself a glorious church, not having spot, or wrinkle, or any such thing; but that it should be holy and without blemish (Ephesians 5:27 KJV).
how can the person be saved in the day of the Lord Jesus Christ by delivering
such person to Satan for the destruction of the flesh?
We see in 1 Corinthians 5:5 that Paul calls for the sinners to be handed to Satan for the destruction of his flesh so that his spirit can be saved. The devil is not supposed to save souls, and it seems anomalous that Paul would expect the devil to destroy a person's flesh but save his soul. This exhortation may well involve excommunication or expulsion from the church, but that still does not explain how this would save the person's soul.
This passage uses is the Greek word for 'Satan', not 'devil', so it is useful to look at pre-Christian Jewish or proto-Christian (pre-gospel) usage of the word Satan, and avoid reading into the passage any meaning that may have arisen in later times. While Christianity has come to equate Satan with the devil, rabbinic Judaism regards Satan as the loyal servant of God, tasked to test the righteousness of the faithful. Consistent with this view, in the first New Testament gospel to be written, Mark, Satan tempts Jesus in the wilderness (Mark 1:13), but does not seek to do evil; when Jesus rebukes Peter and calls him Satan (Mark 8:33), he is speaking of Peter as offering temptation, but not as an evil person:
But when he had turned about and looked on his disciples, he rebuked Peter, saying, Get thee behind me, Satan: for thou savourest not the things that be of God, but the things that be of men.
The Book of Job gives us a good portrayal of the kind of Satan that fits the passage in 1 Corinthians 5:5. It describes Satan as doing God's bidding, going to and fro on earth:
Job 1:6-7: Now there was a day when the sons of God came to present themselves before the LORD, and Satan came also among them. And the LORD said unto Satan, Whence comest thou? Then Satan answered the LORD, and said, From going to and fro in the earth, and from walking up and down in it.
God asks Satan whether he has considered Job, an upright man:
And the LORD said unto Satan, Hast thou considered my servant Job, that there is none like him in the earth, a perfect and an upright man, one that feareth God, and escheweth evil?
Satan is sent to test Job, and causes great harm to his family, in an attempt to have Job curse God and thereby demonstrate his unrighteousness. When this fails, Satan causes physical damage to Job's flesh, which ultimately results in him (and the reader) realising his sin of pride and repenting.
This is what Paul seems to be talking about - let Satan test and punish the Corinthian sinners in the flesh and, by their repentance, save their souls. If Paul did not actually have the Book of Job in mind, then he should at least have been aware of the tradition of which the Book of Job forms a part.
This scripture talks about exposing the believer who has fallen back into sin / flesh, to be tormented by the devil. The aim of such torment is to help such a sinner run back to God and plead for forgiveness so that he will have his right standing with God restored. This can be pictured out clearly with the parable of the prodigal son. Through the torment, the prodigal son remembered home and repented of his sins.
His spirit may be saved at the coming of our Lord. This implies that it is not constant that everyone that will fall back to sin and will be disciplined will finally have his soul saved at the last day. It is a probability that the person may repent through the torment or he may not repent, and could perish. Hence that statement of probability may be saved, which is not the same as will be saved.
More often, according to scriptures, God is not interested in the death of a sinner, so His children that fall back into sin are given the opportunity to repent by exposing them to unfavourable conditions that will make them repent and come back to God. The nation of Israel is an example of that. King Saul had his share of the same opportunity when he was chasing David. But he never used it. So finally he perished. David had a share of that opportunity when he sinned and he used it well by confession and repentance of his sins. 1 Corinthians 10:1-12 tells us that just as it happened to those before us, it's an example for us to learn from and not repeat the same errors. So if Saul and other Israelites could not please God and enter His rest because they didn't use the opportunity given them to repent, so shall it be to every believer who falls back to sin today. You will be given the opportunity to repent through the exposure to the devil to torment you. If you use the opportunity right, your spirit will be saved at the Lord's Coming. But if you don't use the opportunity to repent, you will equally perish as a sinner.
So that fornicator in contention may be saved at the Lord's coming depending on whether he repented of his wrong or not.
"The church is supposed to be holy: the bride of Christ spotless and reserved for Him." The Church IS holy and spotless - she is one flesh with her bridegroom - Christ. We are in the Body of Christ when we live 1 Corinthians 10 -
"10 I appeal to you, brothers and sisters,[a] in the name of our Lord Jesus Christ, that all of you agree with one another in what you say and that there be no divisions among you, but that you be perfectly united in mind and thought."
