to my understanding the following is what comprises Sexual immorality.
Male homosexuality, incest, adultery, and bestiality.
I want to know if oral sex is included even if it's done in marriage?
(Note: this answer comes from a reformed, Presbyterian perspective, YMMV)
Sexual immorality is defined pretty clearly by Jesus in Matthew 5:28 (NIV):
But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart.
That puts everyone who managed to live through puberty squarely in the guilty category here. So let's start from there. We're all guilty of sexual immorality, that's the fact. That's not to say that instances of sexual immorality are not serious and shouldn't be dealt with seriously. But just to introduce some levity, we're all guilty here.
Now, you assumed that 4 things fall squarely in this category, I don't want to argue that list, but at least 3 are pretty expressly forbidden by scripture and the fourth falls squarely into lust for the most part so we'll accept the list. But the point of the first passages is that sexual immorality is even broader. It's deeply embedded in our hearts and minds.
Then of course you drop the bomb, is oral sex immoral? I'm actually going to take this a step farther and get the question you're really asking. Is it OK for married Christians to have anything but normal intercourse? But let's handle a side issue first.
Positions on sex before marriage and any kind of sexual contact outside of marriage vary. However, in my opinion (and it's one I share with a pretty wide swath of mainstream Christianity) it's both unwise and immoral to engage in sexual contact or sex prior to marriage. This is a well supported argument and it's made elsewhere on this site, so it's really not necessary to delve into it here.
The crux of this question is whether or not things that are believed to be inappropriate outside of a marriage are appropriate inside of one. For normal vaginal sex, the answer is obvious. One of the functions of marriage is to provide a home for children and well to have kids you've gotta have sex (obvious caveats for in vitro, adoption etc). But what about non-procreatory sex acts?
Let me be clear. The Bible contains no clear prohibitions on non-procreatory sex acts (in fact a couple of passages in Song of Songs may refer to oral sex specifically and in a very positive way). Although being intentional about being non-procreatory when you are culturally obligated to may have disastrous effects (see Onan.)
This makes it up to the man and the woman in the relationship to set boundaries and decide what is right and wrong in the context of their marriage. For that the guiding principal has to be Ephesians 5:5 (NIV).
Submit to one another out of reverence for Christ.
This passage in Ephesians is much maligned in modern society, but the crux is that we should faithfully submit to one another. It's hinged on respect. In the case of your question that means that anything that you do that is outside of the boundaries set in your marriage can and should be considered sexual immorality.
This brings us back to the passage I mentioned at the outset. Sexual Immorality is not something that has strict definitions. If even looking at a woman with lust in your heart qualifies, then the definition is far broader than any specific act or set of acts. In the context of marriage this means that you must work and communicate with your partner to set your boundaries and decide what is welcome and what is off limits between the two of you.
Paul is very clear that sexual immorality is a condition of heart as much as body. He says in 1 Corinthinas 6:
12 “I have the right to do anything,” you say—but not everything is beneficial. “I have the right to do anything”—but I will not be mastered by anything. 13 You say, “Food for the stomach and the stomach for food, and God will destroy them both.” The body, however, is not meant for sexual immorality but for the Lord, and the Lord for the body. 14 By his power God raised the Lord from the dead, and he will raise us also. 15 Do you not know that your bodies are members of Christ himself? Shall I then take the members of Christ and unite them with a prostitute? Never! 16 Do you not know that he who unites himself with a prostitute is one with her in body? For it is said, “The two will become one flesh.”[b] 17 But whoever is united with the Lord is one with him in spirit.[c]
18 Flee from sexual immorality. All other sins a person commits are outside the body, but whoever sins sexually, sins against their own body. 19 Do you not know that your bodies are temples of the Holy Spirit, who is in you, whom you have received from God? You are not your own; 20 you were bought at a price. Therefore honor God with your bodies.
Basically, whenever you are uniting two bodies in spirit you are having "sex." The physical intimacy is the point of sex, and the thing that can be perverted. If, simply put, you join together that which God has not already put together (i.e. in marriage), it is a misuse.
Yes it certainly does fall into the category of sexual immorality. The simple reason is that if you are participating in such an activity then you will uncertainly be thinking sexually immoral thoughts and most likely be causing the other participant to also be thinking sexually immoral thoughts.
Our thoughts are extremely important for in
Matthew 5: 27-28, Jesus said, "You have heard that it was said to those of old, "You shall not commit adultery. But I say to you that whoever looks at a woman to lust for her has already committed adultery with her in his heart.”
As for if it is immoral within marriage I am unsure, but I would leave it to the husband and wife to decide if they feel it is appropriate.
I would like to bring to mind
Romans 6:13, "And do not go on presenting the members of your body to sin as instruments of unrighteousness; but present yourselves to God as those alive from the dead, and your members as instruments of righteousness to God."
Not entirely sure if this relating to a persons body parts but if it is then it could be an indication of whether it is right to use your body in such a way.
I tried to read the other answers but they did not seem to be specific to oral sex they just spoke generally about sex. Wax eagle in passing mentioned oral sex in a positive light but I thought it was odd no one used the s word. I should say before I go further I'm not married I'd like to be married I've never had sex might never have sex I do everything within my power to be asexual that may disqualify my answer in some people perception and thats fine.
1Co 6:9 Know ye not that the unrighteous shall not inherit the kingdom of God? Be not deceived: neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor abusers of themselves with mankind[G733],
1Ti 1:9 Knowing this, that the law is not made for a righteous man, but for the lawless and disobedient, for the ungodly and for sinners, for unholy and profane, for murderers of fathers and murderers of mothers, for manslayers, 1Ti 1:10 For whoremongers, for them that defile themselves with mankind [G733], for menstealers, for liars, for perjured persons, and if there be any other thing that is contrary to sound doctrine;
From G730 and G2845; a sodomite: - abuser of (that defile) self with mankind.
Sexual intercourse involving anal or oral copulation.
The error of Sodom and Gomorah focused on sexual sins grouped into the words unclean, sodomy, fornication and adultery. Sodomy includes oral stimulation. Sodomy is a Bible word in 1Co 6:9 but is not translated as such in the King James Version. The root words him selves mean men in bed so its possible you could say this only applies to homosexuality.
Jud 1:7 Even as Sodom and Gomorrha, and the cities about them in like manner, giving themselves over to fornication, and going after strange flesh, are set forth for an example, suffering the vengeance of eternal fire. Jud 1:8 Likewise also these filthy dreamers defile the flesh, despise dominion, and speak evil of dignities.
Rom 1:29 Being filled with all unrighteousness, fornication[G4202], wickedness, covetousness, maliciousness; full of envy, murder, debate, deceit, malignity; whisperers,
From G4203; harlotry (including adultery and incest); figuratively idolatry: - fornication.
1Co 10:8 Neither let us commit fornication[G4203], as some of them committed, and fell in one day three and twenty thousand.
From G4204; to act the harlot, that is, (literally) indulge unlawful lust (of either sex), or (figuratively) practise idolatry: - commit (fornication).
However you still have the problem of the word Sodom being sodom from Jude 1:7. It is said that they defiled themselves with strange flesh or you could say different and improper affinity. That suggests to me many different combinations of sex not including marital combination of sexual organs. Besides strange affinity you also have the the broad word fornication from which we derive the word porn. Anything not marital relations is fornication.
1Co 7:4 The wife hath not power of her own body, but the husband: and likewise also the husband hath not power of his own body, but the wife. 1Co 7:5 Defraud ye not one the other, except it be with consent for a time, that ye may give yourselves to fasting and prayer; and come together again, that Satan tempt you not for your incontinency.
Jas 4:17 Therefore to him that knoweth to do good, and doeth it not, to him it is sin.
Rom 14:23 And he that doubteth is damned if he eat, because he eateth not of faith: for whatsoever is not of faith is sin.
Despite all the evidences you could say the Bible does not definitely speak of oral sex however your heart might. If you have doubt in your mind that such actions are sinful and you do it anyways you have sinned and must not do it while your heart doubts. The opposite also being true. Because someone says it is right does not override the conviction of your heart because the word does not expressly call it right.
Not sure how I missed out on answering such a fun question, but it's back on the radar now for some odd reason.
What I understand about the issue of oral sex within the context of the marital act is that it is perfectly ok as long as its not the end of the business. Christopher West, the North American spokesman for the Theology of the Body (teachings of Bl. John Paul II about what the the story of creation, the Gospel and the actual makeup of the human apparatus as God created us have to do with each other) writes about this in The Good News About Sex and Marriage, of which I have only skimmed the juicy parts where he explains why oral (and other) sex is licit so long as the end result could produce a child.
Now, Christopher West recently had voluntarily taken a second look at his own teachings and I don't know of he's recanted of this or not. People accused him of getting to pepped up about sex. Still, I don't see how it could be harmful, in the context of baby making to "have a time of it" as they used to say.