This is hard to wrap my mind around for some reason, but didn't Jesus "die for our sins?" I thought that Jesus dying on the cross meant that all our sins were forgiven, if we believe in him.
It isn't a hard concept, but I can see the difficulty when you grow up hearing one thing and suddenly finding out the Bible says something different.
Jesus died for the sins of the whole world, even for those who refuse to believe in Jesus.
"For the love of Christ compels us, because we judge thus: that if One died for all, then all died; and He died for all, that those who live should live no longer for themselves, but for Him who died for them and rose again" (II Corinthians 5:14-15).
"But the free gift is not like the offense. For if by the one man's offense many died, much more the grace of God and the gift by the grace of the one Man, Jesus Christ, abounded to many" (Romans 5:15).
"just as the Son of Man did not come to be served, but to serve, and to give His life a ransom for many" (Matthew 20:28).
"All we like sheep have gone astray; We have turned, every one, to his own way; And the LORD has laid on Him the iniquity of us all" (Isaiah 53:6).
"The next day John saw Jesus coming toward him, and said, "Behold! The Lamb of God who takes away the sin of the world!"" (John 1:29).
"For there is one God and one Mediator between God and men, the Man Christ Jesus, who gave Himself a ransom for all, to be testified in due time" (I Timothy 2:5-8).
"But we see Jesus, who was made a little lower than the angels, for the suffering of death crowned with glory and honor, that He, by the grace of God, might taste death for everyone" (Hebrews 2:9).
"My little children, these things I write to you, so that you may not sin. And if anyone sins, we have an Advocate with the Father, Jesus Christ the righteous. And He Himself is the propitiation for our sins, and not for ours only but also for the whole world" (I John 2:1-2).
Jesus died for everyone. That means the offer of salvation is wide open to everyone who wishes to accept it. No one is excluded.
Yet, that does not mean everyone is saved. "But they have not all obeyed the gospel. For Isaiah says, "Lord, who has believed our report?" So then faith comes by hearing, and hearing by the word of God. But I say, have they not heard? Yes indeed: "Their sound has gone out to all the earth, and their words to the ends of the world." But I say, did Israel not know? First Moses says: "I will provoke you to jealousy by those who are not a nation, I will move you to anger by a foolish nation." But Isaiah is very bold and says: "I was found by those who did not seek Me; I was made manifest to those who did not ask for Me." But to Israel he says: "All day long I have stretched out My hands to a disobedient and contrary people"" (Romans 10:16-21). The problem is not that people did not know that salvation was available. The problem is that many people are too stubborn to accept the offer.
Other people want to accept the offer on their own terms. "Not everyone who says to Me, 'Lord, Lord,' shall enter the kingdom of heaven, but he who does the will of My Father in heaven. Many will say to Me in that day, 'Lord, Lord, have we not prophesied in Your name, cast out demons in Your name, and done many wonders in Your name?' And then I will declare to them, 'I never knew you; depart from Me, you who practice lawlessness!'" (Matthew 7:21-23).
Payment for sin doesn't mean it remains paid if you continue to sin. "Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God" (I Corinthians 6:9-10). Being saved is not a license to continue sinning. "What shall we say then? Shall we continue in sin that grace may abound? Certainly not! How shall we who died to sin live any longer in it?" (Romans 6:1-2). "Act as free men, and do not use your freedom as a covering for evil, but use it as bondslaves of God" (I Peter 2:16).
When a person turns his back on his salvation and returns to the world, he is just as lost as before. "For if we go on sinning willfully after receiving the knowledge of the truth, there no longer remains a sacrifice for sins, but a terrifying expectation of judgment and the fury of a fire which will consume the adversaries" (Hebrews 10:26-27). One example is Alexander, "This command I entrust to you, Timothy, my son, in accordance with the prophecies previously made concerning you, that by them you fight the good fight, keeping faith and a good conscience, which some have rejected and suffered shipwreck in regard to their faith. Among these are Hymenaeus and Alexander, whom I have handed over to Satan, so that they will be taught not to blaspheme" (I Timothy 1:18-20). It appears that Alexander never learned his lesson because toward the end of Paul's life he wrote: "Alexander the coppersmith did me much harm. May the Lord repay him according to his works. You also must beware of him, for he has greatly resisted our words" (II Timothy 4:14-15). Jesus died for Alexander's sins, but Alexander turned his back on the gift freely offered to him.