It was based off of 1 Corinthians 3:16 that states that we are the temple of God and His Spirit dwells in us. Check it out:
In the Old Testament, the place where God dwelled was His Temple. He didn't have a place in men until after Christ. The same way God lived in the temple then, He lives inside of us now, reminding us to honor our bodies (physically, emotionally, mentally/intellectually, and spiritually) because they are holy and set apart for God, our Savior.
So, background: in the Old Testament only the High Priest could go into the Holy of Holys. That place was more special than any other because that was where God dwelled. It was where He was seated. Literally. So in order to go in, you had to go through a veil, be clean (purified), AND be the appointed one, the HIGH PRIEST, which was only done via ceremony. There he would go in and sacrifice an animal as a blood sacrifice for the people before God as a covenant, so God could grant forgiveness. And when Jesus shed His blood at Calvary, He gave us a New Covenant, a new start with the Father. Jesus died once and for all for our sins, but because of that, God now lives in our bodies.
Therefore, physically, since our body is God's temple, the only one that is allowed in (via sex - and I mean all of it, oral, anal, vaginal, skin-to-skin) is the one God allows.
Your vagina is a part of your body, and therefore God's dwelling place, a Holy Place. The only one that is supposed to ever be allowed in is the ONE high priest, the man God has to be your husband. That man will be anointed by ceremony (your wedding day & marraige) to enter into that covenant with you. Why call it a covenant? Because whenever there was bloodshed, it made a covenant (see above).
Our vaginas come with something called a hymen. Once it breaks, it spills blood over the penis--a blood covenant between husband and wife. This is why God desires sex between man and woman only. Because it's about a COVENANT, not just pleasure. It's about creating a dedication to each other and the Lord before men in a marriage ceremony (just as witnesses watched the priest be anointed). It's about dedicating your life and your marriage to serving & showcasing God and His Kingdom.
So, recap, in order for a man to go into your Holy of Holys, he must go through a veil (hymen), be clean (purified/virgin), and be the appointed one via ceremony (your husband). When we have sex outside of marriage, it's like having an orgy in the house of God! It's not what God wants or desires for us.
This conversation totally transformed my view on sex, like Romans 12:2 tells us to do. I tell you what....I want sex. I'm not gonna say I don't because I want it a lot. But I want more than JUST sex. Right now, I have a distaste for just sex; I don't desire just sex at all. I want a covenant. I want something sacred, holy, special, soul-deep (and something, I'll admit, mind-blowing, titillating, and indescribable lol).
Now, don't get all down by some of the remarks here; technically I won't qualify for a "blood covenant" as there is no longer any veil for me...I am VERY far from being a virgin. But a great thing about this Kingdom living thang is that in Christ we are made new. Old things we did in the past are washed away, and we have a fresh start in Christ. Christ is calling us to move forward, and just not make the same mistakes moving forward. The Holy Spirit will remind & convict us of wrong and help us choose the path away from temptation. But even if we stumble, God's grace still washes us again and restores us. It's just God's desire that we not use Grace as an excuse to sin over and over and over again. (Romans 6:1)
Thank you, Brittany Turner, for your wonderful insight that made this post possible.