Matthew 5:32 But I say to you that every one who divorces his wife, except on the ground of unchastity, makes her an adulteress; and whoever marries a divorced woman commits adultery. RSV
This type of unchastity concerns the degree of relationship between the two married persons.
These couples were never truly married in a Christian sense, such as father and his own daughter or a mother and her son being married together. These types of marriages were sometimes made between pagans during the time of Christ.
However, the following type of relationship is not even tolerated among pagans:
1 Corinthians 5:1 It is actually reported that there is sexual immorality among you, and of a kind that does not occur even among pagans: A man has his father's wife.
Converts to Christianity who were in unlawful and/or incestuous marriages were permitted to divorce and remarry. This is the only exception for divorce and remarriage under the New Covenant if both spouses are alive. A divorced person may remarry if his/her spouse dies. All married persons remain married until death separates them from their spouses.
Matthew 19:8-12 He said to them, “Moses, because of the hardness of your hearts, permitted 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; and whoever marries her who is divorced commits adultery.â€
10 His disciples said to Him, “If such is the case of the man with his wife, it is better not to marry.â€
11 But He said to them, “All cannot accept this saying, but only those to whom it has been given: 12 For there are eunuchs who were born thus from their mother’s womb, and there are eunuchs who were made eunuchs by men, and there are eunuchs who have made themselves eunuchs for the kingdom of heaven’s sake. He who is able to accept it, let him accept it.â€
The disciples are shocked at Jesus' command against divorce and remarriage and they exclaim that it would be better to not marry at all than to be forbidden to divorce and remarry if they could not tolerate their first spouses.
Jesus answers that remaining unmarried is the best choice only for the persons who are truly called to celibacy. But, He is emphatic in His teaching that if you do get married, you are married until either you or your spouse dies.
Mark 10:2-12 (NKJV) 2 The Pharisees came and asked Him, “Is it lawful for a man to divorce his wife?†testing Him.
3 And He answered and said to them, “What did Moses command you?â€
4 They said, “Moses permitted a man to write a certificate of divorce, and to dismiss her.â€
5 And Jesus answered and said to them, “Because of the hardness of your heart he wrote you this precept. 6 But from the beginning of the creation, God ‘made them male and female.’ 7 ‘For this reason a man shall leave his father and mother and be joined to his wife, 8 and the two shall become one flesh’; so then they are no longer two, but one flesh. 9 Therefore what God has joined together, let not man separate.â€
10 In the house His disciples also asked Him again about the same matter. 11 So He said to them, “Whoever divorces his wife and marries another commits adultery against her. 12 And if a woman divorces her husband and marries another, she commits adultery.â€
It is God who joins people together in marriage and so only He can separate them and He does this by the death of one of the spouses.
Paul repeats this teaching:
1 Corinthians 7:39 A woman is bound to her husband as long as he lives. But if her husband dies, she is free to marry anyone she wishes, but he must belong to the Lord.
Divorce and remarriage was tolerated under the Old Covenant, but it is forbidden to divorce and remarry under the New Covenant. A divorced person may remarry if his/her spouse dies.