I had a question after reading some of your site. You say it is possible to sell your soul to the devil. So is that an example of a sin that is unforgivable by God? And even if it is forgivable does the devil now own your soul anyway so you are still going to hell? So that person would not even be judged, or the judgment wouldn't matter?
There is a distinct difference between unforgiven sin and an unforgivable sin. An unforgiven sin could, in theory, be forgiven but the person needing forgiveness has not taken any action to change his ways and ask God for forgiveness. This is what John spoke about in I John 5:16-17. See the article "A Sin Leading to Death" for more details. An unforgivable sin cannot be forgiven -- not because God is unable to forgive but because the nature of the sin is such that it indicates the person is never going to repent and ask for forgiveness. This is what Jesus spoke of in Matthew 12:31-32.
The Bible doesn't speak of selling your soul to the devil in a direct fashion. However, in speaking of King Ahab, we read, "So Ahab said to Elijah, "Have you found me, O my enemy?" And he answered, "I have found you, because you have sold yourself to do evil in the sight of the LORD"" (I Kings 21:20). In order to gain Naboth's vineyard, Ahab was willing to give away his honor and dignity as king solely to possess a piece of property. The king's duty was to uphold the law, but he broke the law and thus sinned against Naboth, his fellow countrymen, and the Lord God.
In a sense, each time you sin you sell yourself to the devil. In other words, in exchange for the momentary pleasure of sin you are willing to place yourself into slavery to serve the desires of Satan. "Do you not know that to whom you present yourselves slaves to obey, you are that one's slaves whom you obey, whether of sin leading to death, or of obedience leading to righteousness?" (Romans 6:16). Worse, when it comes time to "collect" what we have bought, we discover that all we truly have purchased is death. "For the wages of sin is death" (Romans 6:26).
This is why God speaks of salvation as an act of redemption. Redemption is to buy something back that had been previously sold. "And if you call on the Father, who without partiality judges according to each one's work, conduct yourselves throughout the time of your stay here in fear; knowing that you were not redeemed with corruptible things, like silver or gold, from your aimless conduct received by tradition from your fathers, but with the precious blood of Christ, as of a lamb without blemish and without spot" (I Peter 1:17-19). God is willing to buy us back, not because of any obligation on His part, but simply because He loves us and wants to do so. To take advantage of that offer to purchase us back, God only asks us to do a few simple things which demonstrate our willingness to serve Him. "But God be thanked that though you were slaves of sin, yet you obeyed from the heart that form of doctrine to which you were delivered. And having been set free from sin, you became slaves of righteousness. I speak in human terms because of the weakness of your flesh. For just as you presented your members as slaves of uncleanness, and of lawlessness leading to more lawlessness, so now present your members as slaves of righteousness for holiness" (Romans 6:17-19). See the article "The Living Redeemer" for greater details on this topic.
Everyone will be judged, no matter what sins they have sold themselves to commit. "Therefore we make it our aim, whether present or absent, to be well pleasing to Him. For we must all appear before the judgment seat of Christ, that each one may receive the things done in the body, according to what he has done, whether good or bad" (II Corinthians 5:9-10). There is no exception to this rule. Each one of us will see on Judgment Day that God's sentence for or against us is given with absolute fairness and justice.
Thanks for the great answer. So selling your soul to the devil isn't actually saying it and receiving something, but by not accepting Jesus?
Selling your soul is purchasing what the Devil is offering -- sin. Even people who have accepted Jesus can at some later point resell themselves to Satan. "For it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit, and have tasted the good word of God and the powers of the age to come, if they fall away, to renew them again to repentance, since they crucify again for themselves the Son of God, and put Him to an open shame" (Hebrews 6:4-6). This is one of those cases where a person becomes unforgivable because he has rejected the redemption of Christ.
How do you know if you have done this unforgivable act?
You would know because such a person won't go back. Jesus said, "Enter by the narrow gate; for wide is the gate and broad is the way that leads to destruction, and there are many who go in by it. Because narrow is the gate and difficult is the way which leads to life, and there are few who find it" (Matthew 7:13-14). There is only one way to be saved, but that hasn't stopped a number of people from trying to find their own way into heaven, which will never work. "Nor is there salvation in any other, for there is no other name under heaven given among men by which we must be saved" (Acts 4:12).
So if you go back are you forgiven?
Personally, I've believed in God my whole life, although I haven't gone to church too often recently. Although there was a period when I didn't believe 100% that Jesus was the literal son of God, I always sort of did. I am 26 years old and recently have been thinking my life was empty and have become a true believer again, and I have been trying to learn a lot more about the Bible. Is this a situation where it is impossible to go back?
It is not impossible for you to return. You see that you need to go back. A person who rejects Christ doesn't see any need to return. He is positive he is fine just as he is.
But I wonder if you have gotten as far as you think you did, both before and now. You mention that you believe in Jesus, but your description of yourself is a half-hearted belief. "But without faith it is impossible to please Him, for he who comes to God must believe that He is, and that He is a rewarder of those who diligently seek Him" (Hebrews 11:6). Many people are able to accept that God exists, that He is, but fewer really, truly believe that God is going to judge their lives and reward those who are diligently faithful. I say this because their actions don't match their words.
James discusses this at length. "What does it profit, my brethren, if someone says he has faith but does not have works? Can faith save him? If a brother or sister is naked and destitute of daily food, and one of you says to them, "Depart in peace, be warmed and filled," but you do not give them the things which are needed for the body, what does it profit? Thus also faith by itself, if it does not have works, is dead. But someone will say, "You have faith, and I have works." Show me your faith without your works, and I will show you my faith by my works. You believe that there is one God. You do well. Even the demons believe--and tremble! But do you want to know, O foolish man, that faith without works is dead? Was not Abraham our father justified by works when he offered Isaac his son on the altar? Do you see that faith was working together with his works, and by works faith was made perfect? And the Scripture was fulfilled which says, "Abraham believed God, and it was accounted to him for righteousness." And he was called the friend of God. You see then that a man is justified by works, and not by faith only. Likewise, was not Rahab the harlot also justified by works when she received the messengers and sent them out another way? For as the body without the spirit is dead, so faith without works is dead also" (James 2:14-26). Mere words are not faith. Faith is demonstrated in how a person lives their life.
This is why Jesus said, "If you love Me, keep My commandments" (John 14:15). Unfortunately, people claim to love God and to love Jesus, but they will only do so on their own terms. They don't bother finding out what God wants but instead, will assume that whatever they choose to do God will accept.
For example, when you decided to accept Jesus, did you really make any changes in your life? We all sin (Romans 3:23), so I'm sure you have been involved in things that you know God doesn't approve. Did you stop before? Are you making corrections now? Or are you excusing your behavior and staying the course because you hope that your belief in Jesus is going to make everything all right? "I tell you, no; but unless you repent you will all likewise perish" (Luke 13:3).