What does the Bible say is permissible within a Christian marriage? Are there certain restrictions? What is allowable within the confines of the Bible?
God Created Sex
God did not create sex just for procreation or to have children. God created sex for a husband and wife to enjoy. He made us male and female so that we could enjoy each other within the confines of marriage for intimate relations. When Adam and Eve  were both naked, they were not ashamed. They came together in the union of marriage and must have certainly enjoyed sex. The old Victorian and Middle Ages belief that sex was evil was completely off the mark from what God teaches in the Bible. If we read the Song of Solomon, we can see that marital relations are ordained by God. It is not wrong for husband and wife to enjoy one another and that is how we grow closer together.
The Song of Solomon is rightly named for when a man and woman love one another, they feel like singing. In Song of Solomon 1:2-4 we read, “Let him kiss me with the kisses of his mouth— for your love is more delightful than wine. Pleasing is the fragrance of your perfumes; your name is like perfume poured out. No wonder the young women love you! Take me away with you—let us hurry! Let the king bring me into his chambers.” In verses 10 he writes “Your cheeks are beautiful with earrings, your neck with strings of jewels…my beloved is to me a sachet of myrrh resting between my breasts (13) [and] how beautiful you are, my darling! Oh, how beautiful! Your eyes are doves. How handsome you are, my beloved! Oh, how charming! And our bed is verdant” (vv 15-16). Clearly, these two are passionately in love and it is not wrong to desire your spouse as long as this relationship remains private. There is little doubt that this man was in love, writing that she is “Like a lily among thorns is my darling among the young women” (2:2) and she responds “My beloved is mine and I am his” (2:16).
The Marriage Bed is Undefiled
What did the writer of Hebrews mean when he wrote “Let marriage be held in honor among all, and let the marriage bed be undefiled, for God will judge the sexually immoral and adulterous” (Heb 13:4)? I believe that he is contrasting sexual immorality and adultery with marriage being honorable as long as sexual relations stay between husband and wife. If sex remains within the confines of marriage, it is honorable, but outside of the marriage bed, God will judge those who are sexually immoral or commit adultery. Solomon tells husbands to “Enjoy life with the wife whom you love, all the days of your vain life that he has given you under the sun, because that is your portion in life” (Eccl 9:9) and “Let your fountain be blessed, and rejoice in the wife of your youth, a lovely deer, a graceful doe. Let her breasts fill you at all times with delight; be intoxicated always in her love” (Prov 5:18-19). What a joy it is to have a faithful marital relationship for there is no such intimacy and joy that can be enjoyed between those who are not married.
Warnings to the Sexually Immoral and Adulterous
In the same chapter in Proverbs where Solomon spoke of the joy of sex between husband and wife he warns us about the dangers of sex outside of marriage: “Drink water from your own cistern, flowing water from your own well. Should your springs be scattered abroad, streams of water in the streets? Let them be for yourself alone, and not for strangers with you” (Prov 5:15-17). Why? What is the danger? He asks “Why should you be intoxicated, my son, with a forbidden woman and embrace the bosom of an adulteress” (5:20) so “Keep your way far from her, and do not go near the door of her house” (5:8) because “Her feet go down to death; her steps follow the path to Sheol (or the grave)” (5:5). The rhetorical question is “Can a man carry fire next to his chest and his clothes not be burned” (Prov 6:27)? The answer of course is no. When a person chooses to commit adultery they choosing to suffer consequences. When a fire is kept in its proper place like a fireplace, it is comforting, warms the soul, and is a wonderful experience but when the fire spreads outside of the fireplace, the entire home can burn down. The “home” in this case means that the family can be destroyed by adultery. Whole families may be destroyed and any children in that family are forever changed. Adultery and divorce can alter the way children value marriage and this vicious, deadly cycle can repeat itself from one generation to the next.
Paul says that adultery or sexual immorality as sinning against one’s own body and joining one’s self to the prostitute or adulterer is the same as the two becoming one. He warns us to “Flee from sexual immorality. Every other sin a person commits is outside the body, but the sexually immoral person sins against his own body” (1 Cor 6:18) because “he who is joined to a prostitute becomes one body with her? For, as it is written, “The two will become one flesh” (6:16).
Related reading: What Does The Bible Say About Adultery? Five Important Lessons 
What is Permissible in the Marriage Bed?
This is a very controversial subject. I cannot tell you what is permissible and what is not. I am not your conscience. I will leave that up to you. I will not go into details here in specifics because I don’t want to get too graphic since this website is for Christian families and not just for adults only. Let me say this that it is wise to counsel with a pastor or Christian marriage counselor if you have questions about what many consider gray areas. I can say that viewing pornographic images of videos before or during sex is sin from my perspective from what I understand the Bible says. What type of sex takes place on the marriage bed is for the most part, up to each couple and if both are comfortable with what happens, within reason, there should be no problems. Sexual intimacy should always be a private matter between husband and wife and there are no exceptions to this at all. The idea that some do wife or husband swapping is no less than adultery and sex outside of marriage and that is considered adultery and God will judge those who do such things (1 Cor 6:9, 1). That is why Paul warns us to flee or run from sexual immorality just as James said to resist the Devil and he will flee from you (James 4:7).
The Scriptures are clear. Adultery will be judged by God and those who do such things will not be inheriting the Kingdom of God. That doesn’t mean that someone who slipped up and committed such a sin cannot be forgiven. There are Christians that do sometimes slip and fall into sin but they get back up and repent and ask for forgiveness but when we dive into sin and wallow in it with no conviction, this is dangerous ground to be one. God may give us up to our own sin and stop the conviction of the Holy Spirit and there is the possibility that we can become a reprobate (Rom 1:26). I pray you stay faithful before marriage stay sexually pure and that if you are married, you keep your fire in the fireplace, for no one can take fire to their bosom and not get burned.
Related Reading: 10 Good Christian Marriage Rules 
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