I have read a number of things that you have written, and I find you to be very well spoken, and you explain points very well in an understanding way. However I'm still a little lost. I'm trying to find out if, when two people who have committed premarital sex are married, whether or not that sin is forgiven by and through the marriage. I have found different chapters that talk about how marriage sanctifies both people and through marriage you are sanctified. Granted, my knowledge isn't all that vast but to me that sounds like that's a forgiving thing. I'm looking for more information such as passages, examples and so on. I would truly appreciate any help that you can give me.
Fornication is sex between to people who are not married to each other. When those people get married, it is no longer fornication but it doesn't mean the past sins have been forgiven. It only means that the sin is not continuing.
"Sanctified" means to be set apart for a holy purpose. In addressing a question about whether Christians needed to leave their unbelieving spouses, Paul stated that their marriage was still sanctified. "For the unbelieving husband is sanctified through his wife, and the unbelieving wife is sanctified through her believing husband; for otherwise your children are unclean, but now they are holy" (I Corinthians 7:14). The union is still set apart for a holy purpose, even if those in the union are not both believers. Paul is alluding back to: "But did He not make them one, having a remnant of the Spirit? And why one? He seeks godly offspring. Therefore take heed to your spirit, and let none deal treacherously with the wife of his youth" (Malachi 2:14). The goal is to raise up children who follow God. It is not saying that a unbeliever is saved by getting married to a believer.
The only other passage that I can think of that comes close to what you are referring to is "Husbands, love your wives, just as Christ also loved the church and gave Himself up for her, so that He might sanctify her, having cleansed her by the washing of water with the word, that He might present to Himself the church in all her glory, having no spot or wrinkle or any such thing; but that she would be holy and blameless" (Ephesians 5:25-27). However, here the sanctification is referring to the Christians entering into a covenant with Christ and not that marriage sanctifies the couple. Each Christian is set apart for a holy purpose having been cleansed by the washing of water through the word. This is a reference to baptism. "Now why do you delay? Get up and be baptized, and wash away your sins, calling on His name" (Acts 22:16). Through baptism we are freed from sin and become new creatures (Romans 6:3-7). And thus, we are set apart: "Such were some of you; but you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus Christ and in the Spirit of our God" (I Corinthians 6:11). Hence, we are not talking about marriage, but baptism.
Prior to baptism, a person must repent of his sins (Acts 2:38), which means to change both his attitude toward sin and his behavior. Thus, for a fornicator to become a Christian, he has to give up his fornication. Getting married is one way to make this change. But the forgiveness doesn't come until he is baptized. "He who has believed and has been baptized shall be saved; but he who has disbelieved shall be condemned" (Mark 16:16).