God created sex in many life forms. It’s like a mandate by God for all to observe. We have a tendency to think only that God created sex for the propagation of the life forms, and we don’t think about the Oneness from two enacted by many couples. Oneness is truth of the one God. God’s truths have rewards.
Why does God require marriage before sex? I believe it to be liken unto staying with Oneness. An enactment of staying with our Savior, Christ Jesus, the Son of God who is God among us.
The general purpose of sex is to be a convergence unto the one God. Since we live in a broken and fallen world, the sinful ones must die out. Consenting sex with another of the opposite gender has been a selective process; thereby, eliminating some sinful ones. We live in a world of continual flux; changing at all times. Within those changes, we have convergences and divergences. Convergences unto oneness is conducive to believing in one God. So, God rewards the truth of oneness during the act of sex. Although, the flesh profited nothing we are conditioned unto oneness which is conducive to accepting the truth of one God, and marriage makes conducive to keeping the belief in God.
Sex is better in the spirit of Christ Jesus, our Lord. I would venture to say that sex has its optimum in the Spirit of the Lord.
Keep convergencing in glory people.
In this same way, husbands ought to love their wives as their own bodies. He who loves his wife loves himself.