I have written a number of times about marriage, especially about the oxymoron “same-sex marriage.” Do a search on the word “marriage” to find them.
Marriage is a social matter; societies formalize and recognize marriages within a society. There have been significant differences between societies, such as including polygamy or not. Modern societies have civil procedures to ensure the minimum qualifications are met: age, sex, and no other concurrent marriage. Recently this has been relaxed so that sex is no longer a requirement for civil marriage in many countries.
Christianity honors marriage and acknowledges that it was established by God for our first parents. But marriage remains primarily a social matter: it is society that decides who is married and who is not. While same-sex marriage expands the concept of marriage to an extreme, if that is what a society decides, then members of that society should accept that, though not necessarily approve of it. Such a dilution of marriage is worse than polygamy, which has been widely condemned.
What is most difficult about this is the misapplication of the language of marriage. It is like society deciding that parents are no longer mother and father but parent 1 and parent 2 — which is taking place in some birth certificates (see here and here). Will Mommy and Daddy be replaced by Oney and Twoey? The long tradition of marriage between a man and a woman cannot be jettisoned so easily; it will no doubt return someday.
What is Christian marriage? Jesus speaks about marriage and adultery in Matthew 19:
Mt 19:8 [Jesus] said to them, “Because of your hardness of heart Moses allowed you to divorce your wives, but from the beginning it was not so. 9 And I say to you: whoever divorces his wife, except for sexual immorality, and marries another, commits adultery.”
10 The disciples said to him, “If such is the case of a man with his wife, it is better not to marry.” 11 But he said to them, “Not everyone can receive this saying, but only those to whom it is given. 12 For there are eunuchs who have been so from birth, and there are eunuchs who have been made eunuchs by men, and there are eunuchs who have made themselves eunuchs for the sake of the kingdom of heaven. Let the one who is able to receive this receive it.”
This shows that there is a higher definition of marriage, what some would call Christian marriage, which does not include divorce except for sexual immorality. But what if Moses, or the civil law, permits divorce? Jesus does not reject Moses, but as with other passages, the words of Moses are raised to a higher level. Consider another passage about adultery from the Sermon on the Mount:
Mt 5:27 “You have heard that it was said, ‘You shall not commit adultery.’ 28 But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart. 29 If your right eye causes you to sin, tear it out and throw it away. For it is better that you lose one of your members than that your whole body be thrown into hell. 30 And if your right hand causes you to sin, cut it off and throw it away. For it is better that you lose one of your members than that your whole body go into hell.”
Jesus raises the commandment so high that it is impossible for fallen human beings to meet it. This is called the first function of the law: to show us the perfect righteousness of God and our own sinfulness and shortcomings. Similarly, a higher standard for marriage may apply to leaders in the church and others in a position of authority or influence so that the witness of the church is not compromised.
This higher definition of marriage, Christian marriage, adds additional requirements to society’s definition: it must between a man and a woman, and divorce is forbidden except for sexual immorality. But not everyone can receive this definition; only those to whom it is given. There is no implication that the marriages recognized by Moses, or the civil law, are not real marriages. They are real marriages, but lack the additional requirements that would make them Christian marriages.
Those who are divorced and remarried according to the civil law are not living an adulterous life, but their marriages might not be considered Christian marriages. They should be accepted into the church without condemnation, though they might not be qualified for a position of leadership.