Can someone lose their salvation if they want to??? I mean, they whole heartedly got saved, and then doubted and wanted to go Muslim, or something. Are they still saved if they chose not to believe in Jesus as God after they got saved?
God's may chasten in several ways. In 1 Corinthians 11:30, Paul said that in the church at Corinth some were living in sin and in doing so not "discerning the Lord's body." This meant they were calloused towards the fact that Jesus had to suffer for all a person's sins, both before and after they were saved. It did not concern to these believers that Jesus had to suffered for their sin they committed daily. These "undiscerning" believers were not fighting sin, but enjoying sin's pleasures. They were sinning without any regard for how Christ had to suffer for them on the cross. Thus, Paul said, "For this cause many are weak and sickly among you, and many sleep." God had taken the life of some of these unrepentant sinners and others were being chastened with sickness. The Lord was seeking to show them the seriousness of their blatant sin so they might turn from it. However, if chastening such as sickness was ignored, God took their lives to stop them from sinning and to end their destroying their testimony and that of the local church. A church that has members who are publicly sinning will have a poor testimony in the community for the Lord. Thus, the sin that brings on chastening seems to be one that is public and effects not only the Christian's testimony, but the testimony of the local church.
John instructs a congregation not to pray for a member who is callously sinning and refuses to repent. "If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death: I do not say that he shall pray for it." (1 John 5:16)
John makes a distinction between the believer's occasional failures that cause sin and habitual sin that is unconfessed. 1 John 1:8-10 is instruction for the believer to deal with sin in his life.
"If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness. If we say that we have not sinned, we make him a liar, and his word is not in us." (1 John 1:8-10)
Believers are to activity fight sin and resist the temptation to sin. When sin is confessed, which means is admitted, God gives strength for the sin to be overcome. 1 Corinthians 10:13 says that "There hath no temptation taken you but such as is common to man: but God is faithful, who will not suffer you to be tempted above that ye are able; but will with the temptation also make a way to escape, that ye may be able to bear it." A Christian can overcome sin by accepting God's provision that is offered each time one is tempted. A believer is to "And be not drunk with wine, wherein is excess; but be filled with the Spirit." (Ephesians 5:18) God has made able provision for His children to overcome sin.
1 John 5:17 states, "All unrighteousness is sin: and there is a sin not unto death." This is a chilling statement.
Although 1 John 5:16 uses the indefinite article "a" sin, meaning this is referring not a single particular sin, but is certain serious sins that person may commit and not confess. There is "sin" (singular) that can lead to death. This is not the "unpardonable sin" of the Old Testament which is mentioned in the Gospels in Matthew 12:31-32, Luke 12:10, and Mark 3:28-29. The unpardonable sin is in context was a part of the dispensation of the Law of the Old Testament. It is a specific sin of blasphemy, in which a person would credit the devil for the work of the Holy Spirit as the Jewish religious leaders did referring to Christ's miracles. The special circumstances involved in blasphemy cannot be duplicated today. The Scribes and Pharisees committed this sin in attributing the work of Jesus to the Beelzebub who is Satan. (See Matthew 12:24, Mark 3:22, Luke 11:15)
One conclusion a Christian should make is that a person who "professes" to be a Christian and who lives continually in sin without repentance and there is no chastening in his life, it shows he is not saved. God does not chasten the unsaved who are not His children. However, if a genuine Christian continually sins, God will chasten him and that is evidence he is saved.
What is a person then begins to turn from God and refuses to believe any longer.
Two possible answers to your question:
1. One they were never saved to begin with. They could have prayed a prayer and with a "head" knowledge gave mental assent to the Gospel and asked for forgiveness and salvation. However, Romans 10:10 says "For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation." Saving faith comes from the heart. A person believes with their mind, but conversion and salvation comes when the person in their heart believes. God then changes their life meaning they are "born again" (See 2 Cor. 5:17). God transforms them and makes them new and they are indwelled with the Holy Spirit. So some want salvation, but many are not willing to let God control their lives and follow Him. Jesus said, "And this is the condemnation, that light is come into the world, and men loved darkness rather than light, because their deeds were evil. For every one that doeth evil hateth the light, neither cometh to the light, lest his deeds should be reproved. But he that doeth truth cometh to the light, that his deeds may be made manifest, that they are wrought in God." (John 3:19-21) Lots of people would like to go to heaven, but they are not willing to accept Jesus Christ as their Lord and Savior.
Jesus also said, "Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven. Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works? And then will I profess unto them, I never knew you: depart from me, ye that work iniquity." (Matthew 7:21-23)
2. The person is saved, but goes into sin and turns from the Lord. Believers will sin and God says so.... 1 John 1:8-10 was written to believers....not to the unsaved...(see Chapter 2:1) God saves to the saved.... "If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness. If we say that we have not sinned, we make him a liar, and his word is not in us" (1 John 1:8-10).
If a child of God turns from the Lord the Lord will chasten him. God says there is a sin unto death...which means physical death for believers if they refused to repent (turn from their sin) and confess it to the Lord. God chastens unrepentant believers as Hebrews 12:6-11 clearly teaches. 1 Corinthians 11:29-32 describes the chastening of unrepentant Christians in the church in Corinth. God says they did not discern the body of Christ. That means they lived in open sin in disregard that Jesus had to suffer for the sins they committed every day. They then knowing sin, knowing they are causing Jesus more suffering. God said He chastened these people by making some of them sick and others He had taken their lives. In an act of love God stopped them from continuing in sin and its destructive result by taking their lives.
So to answer you question. I Christian can turn from the Lord, but the Lord will never turn from His child.
1 Corinthians 3:10-15 says at the BEMA judgment all believers will be judged. Those that were not faithful or lived with unconfessed sin in their lives will not receive any reward...but verse 15 says... "If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire." (1 Corinthians 3:15) In other words once a believer is truly saved he cannot lose the salvation God gives to him. He can lose reward and quite honestly many believers will be solely ashamed when they meet the Lord face to face....
When God says that "For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life" (John 3:16) He means "everlasting" or eternal life. If God gives you eternal life....then it is eternal and cannot end. My article should clear up other questions you and your friend might have. God bless you as you study God's word.
I have a message at https://bible-truth.org/1JN5-14-21.html which addresses God chastening Christians.