What is the Biblical basis against same-sex marriage?

The entire Bible can be understood as a metaphor for marriage, and the marriage that the Bible is a metaphor for cannot be understood as a marriage of two people brides or two grooms.

Behold, the Bridegroom cometh, go ye out to meet him. These words were written by St Matthew the Evangelist, and Christ spoke them to His disciples and to all other men in the parable of the virgins. This Bridegroom is Christ, and human nature is the bride; which God has made in His own image and after His likeness. And in the beginning He had set her in the highest and most beautiful, the richest and most fertile place in all the earth: that is, in Paradise. And He had given her dominion over all creatures; and He had adorned her with graces; and had given her a commandment, so that by obedience she might have merited to be confirmed and established with her Bridegroom in an eternal troth, and never to fall into any grief, or any sin

St. John of Ruusbroec (1293-1381) - The Adornment of the Spiritual Marriage

The Bible begins with a marriage, it ends with a marriage. Jesus starts his ministry off at a marriage. St. Paul uses matrimonial analogies to understand Christ's headship of the Church. No part of the lens by which marriage could be comprehensible with a Biblical worldview can find its sufficiency in anything but marriage between the sexes.

But, just as society has made analogies to fatherhood impotent, and modernity has made analogies to kingship futile and economics has rendered analogies to agriculture fruitless, progress has done a number on sex and marriage as far as Biblical analogies go. Hence, this question, which itself would have been incomprehensible at the inception of Christianity stackexchange a mere ten years ago makes nothing but sense to ask now.

1st Corinthians 6:9-11 seems to indicate such:

9 Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived: neither the sexually immoral, nor idolaters, nor adulterers, nor men who practice h*m*sexuality, 10 nor thieves, nor the greedy, nor drunkards, nor revilers, nor swindlers will inherit the kingdom of God. 11 And such were some of you. But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God. (ESV)

" ... Can it be ordained of God?"

The question which has been asked hinges on what is ordained of God.

If something other than what is ordained is done, then it will not be authorised and will fall under condemnation.

NOTE: the above question has not defined what 'marriage' actually is, nor has the question defined what 'sex' means, within the larger term 'same-sex'.

The definition of marriage in the bible is that given first by Adam :

Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh. [Genesis 2:24 KJV]

This is reiterated by Jesus of Nazareth :

For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh? [Matthew 19:5 KJV]

This is how marriage is defined in the bible.

The term 'husband' in both Hebrew and Greek is grammatically male.

The term 'wife' in both Hebrew and Greek is grammatically female.

How these words are interpreted, may be a matter of argument, depending on one's view of language as such, or depending on one's view of the concepts expressed by the language, or depending on one's view of the technicalities involved in the two states.

Similarly, the term 'marriage', itself, may be argued about as to what it is, what it represents, and what is its function, and what are the parameters which govern the state of marriage.

There is no other definition available, in the bible, so this is how marriage must be conducted by persons who follow Jesus Christ and by persons who, though not followers of Jesus Christ, wish to adhere to God's word as made known in the Hebrew scriptures.

Various countries in the world today have a variety of laws and that is an individual matter for the Governments (and the citizens) of those countries.

But those who would wish to follow Jesus Christ have his word to follow as to their conduct in the matter of marriage.

Generally speaking, the word of God to Israel was not addressed to other nations, though nations could follow it, if they wished.

Similarly, the whole breadth of the word of Jesus Christ is not addressed to the nations, though anyone, in any country, may follow his word, if they wish.

Specifically, Jesus' words are addressed, via his apostles, to the nations, but only those who, from among those nations, are baptised (see Matthew 28:20) are further taught and instructed by those same apostles (or the resulting, contemporary, apostolic ministry) to hear and to obey the entire content of the speech of Jesus Christ.

The matter of baptised persons marrying would be a matter of voluntary obedience to the words of Jesus Christ in the context of a Body (the Church) which is instructed by the apostolic ministry, walking in the word and in the steps of the apostles.

Any particular society (called, usually, a 'church') would be voluntarily self-governing and membership would be both voluntary and also a matter of societal approvement.

Thus marriage within that voluntary body would be one of voluntary obedience within the context of that particular society, whether local or more widely corporate.

In the matter of another ordinance (the covering of the head) Paul states certain arguments (the Headship of Christ, the witness of angels, the relative status of male and female in the church) encouraging the practice but ends his coverage of the ordinance by saying :

If any man seem to be contentious (to the ordained requirements) we have no such custom (that is, to disobey the ordinance) neither the churches of God. [1 Corinthians 11:16 KJV]

Thus Paul the apostle of Jesus Christ makes it clear that what the churches regard as a customary ordinance is what they will do, irrespective of others who do not agree with it.

Volition works both ways : one may voluntarily include oneself by obedient agreement or one can voluntarily exclude oneself by refusing what is enjoined, by custom, upon all.

It is also relevant that in that same passage (addressed to the church in Greece) regarding an ordinance affecting male and female, Paul states 'doth not even nature teach ...' so it is clear that Paul sees certain matters (in context, regarding male and female) to be judged according to what 'nature' teaches.

In another epistle, addressed to other readers (the church in Rome) Paul dictates to Tertius, his scribe, that he regards certain things as a matter either of 'natural use' or behaviour that is 'against nature'.

Thus if one wished to follow Jesus Christ in the way in which Paul did so, one would have to take the matter of 'nature' (or rather what Paul regarded as 'nature') into account.

Put briefly, whenever the Bible refers to marriage, it is clear that it is about the union between a male and a female, a husband and a wife, not between individuals of the same sex. Therefore, the concept of a same-sex marriage is foreign to the Bible.

24 Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh. [Genesis 2:24 ESV]

5 and said, ‘Therefore a man shall leave his father and his mother and hold fast to his wife, and the two shall become one flesh’? [Matthew 19:5 ESV]

6 But from the beginning of creation, ‘God made them male and female.’ 7 ‘Therefore a man shall leave his father and mother and hold fast to his wife, 8 and the two shall become one flesh.’ So they are no longer two but one flesh. 9 What therefore God has joined together, let not man separate.” [Mark 10:6-9 ESV]

22 Wives, submit to your own husbands, as to the Lord. 23 For the husband is the head of the wife even as Christ is the head of the church, his body, and is himself its Savior. 24 Now as the church submits to Christ, so also wives should submit in everything to their husbands.

25 Husbands, love your wives, as Christ loved the church and gave himself up for her, 26 that he might sanctify her, having cleansed her by the washing of water with the word, 27 so that he might present the church to himself in splendor, without spot or wrinkle or any such thing, that she might be holy and without blemish. 28 In the same way husbands should love their wives as their own bodies. He who loves his wife loves himself. 29 For no one ever hated his own flesh, but nourishes and cherishes it, just as Christ does the church, 30 because we are members of his body. 31 “Therefore a man shall leave his father and mother and hold fast to his wife, and the two shall become one flesh.” 32 This mystery is profound, and I am saying that it refers to Christ and the church. 33 However, let each one of you love his wife as himself, and let the wife see that she respects her husband.

[Ephesians 5:22-33 ESV]

Now concerning the matters about which you wrote: “It is good for a man not to have sexual relations with a woman.” 2 But because of the temptation to sexual immorality, each man should have his own wife and each woman her own husband. 3 The husband should give to his wife her conjugal rights, and likewise the wife to her husband. 4 For the wife does not have authority over her own body, but the husband does. Likewise the husband does not have authority over his own body, but the wife does. 5 Do not deprive one another, except perhaps by agreement for a limited time, that you may devote yourselves to prayer; but then come together again, so that Satan may not tempt you because of your lack of self-control.

[1 Corinthians 7:1-5 ESV]

Furthermore, the times the Bible does refer to same-sex romantic relationships, they are portrayed in a very bad light:

26 For this reason God gave them up to dishonorable passions. For their women exchanged natural relations for those that are contrary to nature; 27 and the men likewise gave up natural relations with women and were consumed with passion for one another, men committing shameless acts with men and receiving in themselves the due penalty for their error. [Romans 1:26-27 ESV]

9 Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived: neither the sexually immoral, nor idolaters, nor adulterers, nor men who practice h*m*sexuality, 10 nor thieves, nor the greedy, nor drunkards, nor revilers, nor swindlers will inherit the kingdom of God. 11 And such were some of you. But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God. [1 Corinthians 6:9-11 ESV]

Many find the combination of these two independent arguments quite compelling. At least I do.