This issue has come up countless times since this sub started, and I suspect it will keep coming up. For the purpose of enforcing Rule 7, let me be clear: any encouragement that someone engage in sex outside of marriage will be deemed a rule violation, the comment will be removed, and the person potentially temp or permabanned, depending on the context.

That said, legitimate conversation about the following are still perfectly acceptable: (1) whether or not it is actually sinful, (2) why God or the church believe it is sinful, (3) the practical and spiritual ramifications on life if one side or the other is true (ex. if it weren't sinful, let's explore what that would look like), etc.

Old Testament

The first thing to note is that marriage itself is defined by two things: (1) two people becoming one flesh (i.e. sex) and (2) a mutual covenant. The mutuality of that covenant in biblical times didn't even have to be between the people having sex - it could have been between the groom and the bride's father, for example. All that matters is that there is sex and a covenant.

Exodus 22:16-17 is a great example of this. The ordinary flow was bride price > marriage > sex. If someone violated this order by skipping straight to sex, he was obligated under the Mosaic law to go back and fulfill the first two, thereby legitimizing the sexual conduct through the bride price and marriage. Even if the marriage was refused (i.e. no covenant), the bride price for a virgin still had to be paid. This should make it clear that at least for Israel's society before the time of the Kings (i.e. when God made the laws rather than man), it was considered a violation of the law to have sex with someone outside of a (1) bride price and (2) marriage.

Note that this doesn't read like, "Park anywhere you want, as long as you're willing to pay the parking ticket." It's more like, "It is against the law to park there. If you do park there, you will have to pay a parking ticket." To that end, Exodus 22:16-17 is not an authorization to have sex outside of marriage as long as you're willing to pay the price; it's a condemnation of the practice, the penalty for which is the bride price and an obligation into marriage.

I should also note that I lean toward the view that if two people intentionally and with consent engage in becoming one flesh, then this intentional consent satisfies the "covenant" component. Accordingly, "premarital sex" isn't really even a thing - it's more "pre-ceremony sex." The reason I lean toward the view (I can still be persuaded otherwise) that intentional consent implies a covenant is because the act of becoming one flesh is clearly reserved for marriage (as this entire post demonstrates), and thus an intention to engage in such an act implies the covenants that are associated with the marriage context within which the sex is meant to occur. It's like going to the bar and ordering a drink. The context of your behavior implies that you understand and are bound to the covenant of paying for that drink. It is a contract by conduct (which is recognized even under most every modern legal jurisdiction and not just in ancient Israel) rather than by express words. Accordingly, if two people try to engage in sex without having a ceremony, they should be held to the legal requirements of marriage (under God's law, not man's) and treated as though they are married. This, if true, resolves the entire debate about premarital sex in full - because there would be no such thing as premarital sex, except in the case of non consensual sex.

New Testament

Now, there are several other OT passages I could dive into, but I don't like delving too much into the Mosaic law because that was really only applicable to Israel. Given that I'm not an Israelite in the time of Moses, there are certainly principles I can learn about God from the laws he established, but they are not by any means binding to me today as a non-Israelite. So, what else does the Bible say?

Jesus' framing of the issue is fairly telling. He gives the famous "except for porneia" line after which the disciples marvel at the severity of the restriction. Accordingly, this concept of porneia - whatever it means - is not meant to be interpreted in a way that makes it easier to get divorced. That is; Jesus meant a very narrow thing when he said that, which would cause the disciples to have the sharp reaction they did. But more interesting is that Jesus' response to the conversation is to skip straight to indefinite celibacy, as if those are the only two options. Either you get married, or you remain celibate. We can't really read a middle-ground in the way Jesus is talking about this. This tells us that Jesus' frame of mind was that sex outside of marriage is sin.

In 1 Cor. 7:8-9 Paul says that the unmarried and widows should actually stay single. However, if two people are burning with passion for one another, it is better to marry. If they were able legitimately to have sex without getting married, given Paul's extremely strong language in the rest of this chapter against marriage, I can't imagine Paul would have recommended marriage in that situation when "sex while staying single" was an option. This tells us that Paul's frame of mind was that sex outside of marriage is sin.

Neither of them were quoting the old testament LAW when citing these conclusions or establishing the context for expressing their frame of mind. Jesus cited the order of creation as the context for his assertion and his only reference to the law was in response to a question that was asked - and then he creates a direct contrast from his position from the technical legal conclusion, demonstrating that the OT law is not the basis for his opinion and mental framework on the issue.

It is also interesting, of course, that prostitutes were condemned as sinners. Most prostitutes' only crime was that they had sex outside of marriage. We're not talking about bestiality or objectophilia or other perversions, for which they would not have been paid. We're simply talking about sex outside of a marriage context - and yet they were considered sinners. We don't see Mary Magdalene going back to her old ways after finding Jesus. 1 Cor. 6:15-18 actually notes a clear imperative not to have sex with a prostitute, stating that this would be like trying to unite Christ with her. Paul didn't contemplate that the prostitute might be a Christian because he assumes that any Christian would have repented from prostitution (i.e. a lifestyle of sex outside of marriage), further evidencing Paul's mental framework regarding sex outside of marriage while writing his epistles.

Reflecting the Image of God

Direct passages aside, there's also a general spiritual framework for understanding the issue. As Ephesians 5 informs us, the husband-wife relationship is parallel in scripture with the relationship between God and his people (today: Christ-church, but it also applied in Israel, per numerous OT passages). Accordingly, if we want to understand appropriate boundaries for physically reproductive acts (i.e. sex), we can look to the example God sets for us in how he engages in spiritual reproduction.

Simply put: God does not reproduce with non-believers. Matthew 7 makes it clear: "No bad tree produces good fruit." We do see God using non-believers for his purposes, but we don't see the Spirit indwelling them for evangelistic intent with any success. So, if a man were to enter into a woman in a reproductive act, this would violate the parallel image of God that our physical conduct should be reflecting about His character.

Now, one could easily argue, "That's why we use protection - that way we're not producing fruit outside of marriage" and that the "having kids within marriage" concept is what's really spiritually protected. But this fails to do justice to the effort involved and the uncertainty associated with many forms of "protection." We don't see God indwelling with a non-believer at all - not in the same way he does with believers, at least. We see an external drawing toward himself and subtle nudges in appropriate directions. But when Romans 8:9 references an indwelling Holy Spirit, that's only for believers who are known as Christ's bride - and by extension, a man entering into a woman is only for his bride.

Don't Fall Into the Linguistic Trap

Some will try to argue that the Greek and Hebrew words in the passages usually referenced regarding premarital sex are more general terms for "illicit sexual activity," and don't specifically refer to premarital sex, and therefore premarital sex isn't explicitly rejected. This fails for two reasons.

First, there are lots of things not directly mentioned in the Bible, which we know to be sinful today. In fact, the Bible contemplates this in Romans 1 where it says that the person with the depraved mind "invents new ways of doing evil." Watching videos of child pornography on the internet didn't exist in biblical times, but it certainly would have fallen under some other category of sin, including "illicit sexual activity." I can hardly imagine anyone making a case that posting videos of minor children engaging in sexual activity on the internet does not fall into the category of "illicit sexual activity." Virtually everyone agrees about this, right? So, who decides what falls under porneia (or other words used for "fornication") and what doesn't? It seems arbitrary for someone to determine that child porn does, but premarital sex doesn't. What standard is being used to create that distinction?

Second, and in partial response to the above, it matters what people would have understood by the words being communicated at that time. We must assume that Jesus believed his intended audience would understand what he meant when he used certain words. This is clear from Matthew 13:13-17, where Jesus says directly that there are some people who he doesn't want to understand what he's saying, but others who he does intend to understand plainly. We have no reason to believe that his disciples were among the crowd he intended to confuse with his words when he talked about sexual immorality. So, what would these people have understood by the word porneia and other other such words associated with premarital sex? They would have known the common use of those words at that time, which includes premarital sex as being within the scope of the word. This is evidenced by countless literary texts including those outside the Bible which utilize those words to reference sex among non married persons. We cannot ex post facto remove a common understanding of a word in one time period and say, "Well, today we don't mean it that way, so the meaning of the Bible changed when our human dictionaries changed." Whether premarital sex is considered "illicit" today has no bearing on whether it was considered porneia 2,000 years ago.

Conclusion

There are, of course, countless other arguments that I do not have the time or interest to go through. However, for the purpose of this sub: premarital sex will be deemed "sin" and it will be a rule violation for anyone to recommend it.

If anyone wants to debate the merits of this position, be my guest. However, in the absence of a retraction, this rule remains.

That said, there is also great grace and love for those who have engaged in premarital sex. The Bible gives incredible judgment and condemnation against those who continue in willful, defiant, unrepentant sin ... so don't go there. But if it's part of your past, it's part of your past. We'll take you as you are in the face of repentance and never look back, except to the degree that your past may have practical (as opposed to spiritual) ramifications on your future.