Question:I just read over your response to a girl who lives with her boyfriend and she asked why you called it a sin. You gave her reasons, but then you listed reasons for her to consider. The second heading was "It Can Keep You Out of Heaven." If you are preaching the truth as you say, you should have told her that if she has accepted Christ as her Savior and believes he died for our sins and was raised again, she'd be forgiven.
The question being addressed was why fornication is called a sin. The young woman also made it clear that she saw no reason for getting married. Therefore, I addressed the question of why living together without marriage a sin.
All sins can be forgiven, but your answer is not nearly complete. For example, your answer implies that she could remain in her sin, continue to commit fornication, and be forgiven. This is not what Jesus taught. "I tell you, no; but unless you repent you will all likewise perish" (Luke 13:3). Turning away from sin, repentance, is absolutely critical to receiving forgiveness of sin. Peter also stated the same. "Then Peter said to them, "Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit" (Acts 2:38).
Peter brings up another point that you left out. God has never taught that salvation is by just faith alone as you imply. In fact, God teaches the opposite. "You see then that a man is justified by works, and not by faith only" (James 2:24). Actions must match the faith, else the faith is dead. One must have faith in Jesus and his death for our sins. So what action does God require to match that faith? "Or do you not know that as many of us as were baptized into Christ Jesus were baptized into His death? Therefore we were buried with Him through baptism into death, that just as Christ was raised from the dead by the glory of the Father, even so we also should walk in newness of life. For if we have been united together in the likeness of His death, certainly we also shall be in the likeness of His resurrection, knowing this, that our old man was crucified with Him, that the body of sin might be done away with, that we should no longer be slaves of sin. For he who has died has been freed from sin" (Romans 6:3-7).
The woman who wrote needed to be convicted of the fact that she was living in sin. Only then would she be willing to repent of those sins and seek forgiveness. If she had responded, I would have continued with what she needed to do to gain forgiveness. As it stood, she didn't believe she was in sin and thus believed she had no need for forgiveness.
On your part, you need to start teaching the full gospel of God instead telling people that God accepts people who remain in their sins and refuse to obey His commands.