How would Reformed Christians deal with homosexual marriage of individuals prior to their conversion to Christianity?

Most European Reformed Churches welcome gay and lesbian members.

The United Church of Canada was the first to accept same-sex marriage and confirmed to stay to this in 2007

The Reformed Church of Switzerland has decided to tolerate h*m*sexuality in 1999 see here (German) and allows h*m*sexual marriage since 2019 see here (German).

The Reformed Church of Germany has decided to offer public blessing to h*m*sexual couples quite recently, see here (German).

Other Churches (Netherlands, Scotland, ...) are currently in discussion.

The above views may be correct for the Reformed Church of America (USA) who takes the position that h*m*sexual sexual activity is sinful.

An overview is given on Wikipedia here and here

Many conservatives would like to have their cake and eat it too in regards to marriage. They wish to defend the "sanctity" of marriage stating that God ordained it as something sacred between 1 man and 1 woman; as if God somehow supernaturally preserves and defines the definition of marriage but let us consider for a moment that there are many heterosexual couples who are not Christian but are married. Even within the confines of a biblical interpretation, marriage has not always been between 1 man and 1 woman, but in the past was between 1 man and many women, so clearly the definition of marriage was in flux in scripture in the past and could therefore presumably undergo a change again. Would we deny secular couples their marriages because they were apart from God? Are they not married because they were not married before God, but instead married before a Justice of the peace? Do they need to remarry if both members of the couple become Christian?

Clearly these secular marriages are not denied by most religious persons and if the secular marriages are valid and real apart from God, then the definition of marriage also exists apart from God. Otherwise, non-christians should simply divorce their partner when one member of the couple becomes a Christian.

Because of this, So long as secular marriages are recognized as valid by Christians, they should continue to allow gay men and women to marry too. This is because it is not God or the Bible which defines what a marriage is. As such, I would suggest that when applied to a gay couple, their marriages continue to be recognized.

We should then apply 1 Corinthians 7:12-14 equally. The Bible teaches that we should not marry the unbeliever (2 Corinthians 6:14, Deuteronomy 7:1-4) and therefore if you married an unbeliever but continue to be in a relationship with them you are "living in sin" yet Paul tells us in 1 Corinthians we should remain with that unbeliever. As Paul seems to recognize these secular marriages, we should to. Paul recognizes these marriages because our obligation to our vow to our significant other supersedes all other considerations. The obligation to our vow does not change simply because the gender the partner does.

As an aside, by denying secular couples the right to marriage aren't we forcing them to further live in sin by forcing them to commit adultery in addition to their "sin" of sodomy and should we cause others to stumble in this way?

You're not going to like this answer, but that's because I think the premise is flawed. Why is h*m*sexuality given a standing all its own? What's wrong with the other hundreds of works and confessions by Reformed thinkers regarding sin?

The question is not one of legality, but one of morality. Speaking from a Reformed Baptist perspective (I know, not truly "Reformed"), such individuals would be welcomed as any sinner would. They may attend services and worship freely and should be unharried in their attendance. They are to be treated lovingly, as any other individual would be treated. They must be presented the true gospel, God's grace apart from works of the flesh, just as any sinner would.

However, the union is not recognized as a sanctified union before God (I don't feel the need to defend this here. It's worth a question all its own) and as such, the couple is to be viewed as two individuals. They should not be considered for any counsel, nor should they be encouraged to partake in the ordinances so long as they willfully consider themselves to be in a union.

Such a couple should not be made an example, and at the same time teachers must not shy away from teaching the hard truths in the scriptures that a h*m*sexual union was not given as an object lesson of Christ's work but rather a singular heterosexual marriage is (divorcees who have remarried raise another question, too).

Regarding the legality of the practice and the fact that the union is between two consenting adults, the question is functionally the same as that of prostitution (imagining the church is in a location where such practice is legal) or heterosexual cohabitation apart from marriage. If the convert stops uniting himself with a person who is not his wife, then he is demonstrating the beginning evidence of the Holy Spirit's work in his life and should be treated as a brother (with struggles) and gently examined over time for trustworthiness of the faith. However, if he demonstrates no attempt to stop this practice, he should be treated as one who is not a convert but rather one who needs to hear the gospel.

Edit:

It has been asked "What of h*m*sexual couples who bring children to church? Should they be told to end their legally-separate union?"

First off (and this is the Baptist in me coming out), it is not the church's or church members' prerogative to be telling people what they should and should not do in their personal lives, apart from expositing the scriptures. If a h*m*sexual couple is dependent upon each other financially and also has children, this is something of a unique situation. It is unhelpful to tell them "split up and never see each other again, and give your children up for adoption... again."

Yet we can not shy away from the truth. Speak the truth from the scriptures as you arrive at them. Do not make an example of these people. Pray for them. In God's perfect timing, their eyes will be opened and their minds will no longer think in futility. Incidentally, this is always the answer. All of the other things will work out so long as this precept is first.

If they want to partake in communion or Baptism, it must be explained that their presence in the church is appreciated, but they cannot take the sign of identification with Christ while they have no interest in repentance of their most obvious and public sins. Additionally, one cannot be in communion with the church (through the supper) while in the same position. If they insist on taking communion, they are guilty of profaning the body of Christ and should be repeatedly, gently asked not to take communion and be given an explanation as to why.

If this is enough to push them out of the body, I'm ok with that. Every effort has been made to be inclusive as far as the scriptures permit. It's a bad situation, and either it will turn biblical or it will not. There's not really a lot of middle ground. We must seek God's approval above man's, even if it means losing those who attend a church.

Edit 2:

The edit in the question is applying a context that the passage does not warrant. Being circumcised is not a sin, nor is being uncircumcised. Being married is not a sin, nor is being single. However, a h*m*sexual union is sin and is thus not applicable to the passage. One verse in the section sums it up nicely: For neither circumcision counts for anything nor uncircumcision, but keeping the commandments of God. (1 Corinthians 7:19 ESV)"

John Piper addressed a portion of this question in the context of Minnesota's "Same-Sex Marriage Amendment". Having listened to his sermons on Romans 1 and other statements by him, the following principles are his consistent teaching on the question:

1. Marriage is created and defined by God in the Scriptures as the sexual and covenantal union of a man and a woman in life-long allegiance to each other alone, as husband and wife, with a view to displaying Christ’s covenant relationship to his blood-bought church.
2. There is no such thing as so-called same-sex marriage, and it would be wise not to call it that.
3. Same sex desires and same sex orientation are part of our broken and disordered sexuality owing to God’s subjection of the created order to futility because of man’s sin.
4. Therefore, same-sex intercourse, not same-sex desire is the focus of Paul’s condemnation when he threatens exclusion from the kingdom of God.
5. Therefore, it would contradict love and contradict the gospel of Jesus to approve h*m*sexual practice, whether by silence, or by endorsing so-called same-sex marriage, or by affirming the Christian ordination of practicing h*m*sexuals.
6. The good news of Jesus is that God saves heterosexual sinners and h*m*sexual sinners who trust Jesus, by counting them righteous because of Christ, and by helping them through his Spirit to live lives pleasing to him in their disordered brokenness.

I extracted these from the text of his June 16, 2012 sermon, but left off the last two points that shifted to the Church's attitude toward political action. Piper obliquely addressed the question of what to do if members of this sort of union were to join his congregation:

Churches will be faced with new and unheard of cases of discipline. Suppose two so-called “married” men hear the gospel and one of them believes and comes to your church. Will you council “divorce” and moving out?

He also quoted 1^st Peter 2:12's encouragement to engage the world with honor:

Keep your conduct among the Gentiles honorable, so that when they speak against you as evildoers, they may see your good deeds and glorify God on the day of visitation. (ESV)

I believe we can extrapolate from these principles:

1. Like any other sin, h*m*sexual practice should be resisted. If a new believer continues in their habitual sin, it's the responsibility of the Church warn against the dangers of sin.

2. On the other hand, h*m*sexual desire is like any other temptation. We should not be afraid of it. Christians resist temptation with the power of the Holy Spirit.

3. Same-sex marriage is not binding in the eyes of God and nor should it be binding in the eyes of the church.

So we can safely ignore the teachings on divorce in this case; divorce as understood in the Bible just doesn't apply. Instead, I think the actual parallel is to the state of voluntary servitude. That analogy might seem distasteful, but in the Roman world being a bondservant was actually a respectable position. Many bondservants performed duties that we would recognize as white-collar professions. More to the point, it was a civic obligation that Paul explained was no longer binding to believers.

Here is Paul's advice:

Were you a bondservant when called? Do not be concerned about it. (But if you can gain your freedom, avail yourself of the opportunity.) For he who was called in the Lord as a bondservant is a freedman of the Lord. Likewise he who was free when called is a bondservant of Christ.—1^st Corinthians 7:21-22 (ESV)

Therefore, it seems to me that a Christian who submitted to a same-sex civic contract before they converted should abstain from sexual intercourse, but honor the other obligations of the union. That would include financial and parental duties if applicable. Separation should be seriously considered in order to reduce temptation. If there is an honorable way to nullify the union, that should be pursued. If not, nobody should be concerned about it.

Conclusion

It's very likely we will see some missteps and controversy in the next generation. Our society is increasingly approving of same-sex practice, but the church should not be. I'll let Piper have the final word:

One of the most powerful things we can do is fold into our churches men and women who have same-sex attraction and surround them with a bigger vision of life and love and relationships that make it possible for them to flourish in families and friendships. These stories may be one of the most authenticating messages for the Christian gospel.

A note on civil marriage

Sometime after I wrote this, a friend pointed out I hadn't addressed civil marriage. In some countries (Mexico is one I'm most familiar with), people hold two ceremonies:

1. A religious ceremony in a church and
2. A civil marriage performed by a government official.

In the United States, marriage is governed by state laws which may delegate the authority to perform a marriage to a religious official. So it didn't (at the time) seem to be significant to the discussion. However, I recently read a letter by David French that points out that covenant marriage already differs from civil marriage. In particular, most state laws allow divorce for almost any reason and allow remarriage. Jesus equates that practice with adultery. There are practical reasons to allow more in a civil marriage than in covenant marriage, of course.