After divorce, a person who has known the joys of union in marriage now finds himself alone and longing for companionship again. This is not easy to deal with, because memories do not go away easily. Often a major contributing factor to divorce is a very weak (or absent) relationship with God. Now a person is struggling with loneliness in the same weak spiritual condition, and it takes drastic steps in God to see the direction changed. One of the serious consequences of divorce is that it opens the door for adultery, and God views adultery as an even greater sin than divorce. (Divorce may not be sin if it is forced upon a partner who desires to keep the marriage unbroken, but often it is the outcome of unforgiveness and bitterness—which is sin—destroying the relationship.)
The scripture never tells us that there will be no divorced people in heaven, but it does say that there will be no adulterers there. "Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God" (1 Corinthians 6:9-10). "Marriage is honorable among all, and the bed undefiled; but fornicators and adulterers God will judge" (Hebrews 13:4).
What is adultery? Jesus is very clear about this. "Whoever divorces his wife and marries another commits adultery; and whoever marries her who is divorced from her husband commits adultery" (Luke 16:18). "In the house His disciples also asked Him again about the same matter. So He said to them, ‘Whoever divorces his wife and marries another commits adultery against her. And if a woman divorces her husband and marries another, she commits adultery'" (Mark 10:10-12). "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" (Matthew 19:9).
I quote these scriptures from three gospels to emphasize the veracity of the statements of Jesus. Paul reinforces the matter while writing to the Romans: "Or do you not know, brethren (for I speak to those who know the law), that the law has dominion over a man as long as he lives? For the woman who has a husband is bound by the law to her husband as long as he lives. But if the husband dies, she is released from the law of her husband. So then if, while her husband lives, she marries another man, she will be called an adulteress; but if her husband dies, she is free from that law, so that she is no adulteress, though she has married another man" (Romans 7:1-3).
God did not leave the area to be unclear. Very simply put, adultery (or an adulterous relationship) is a man or woman joining themselves to another person's husband or wife. All of the scriptures above speak about not just an act of adultery, but an adulterous relationship: a second "marriage" (leaving and cleaving) that takes place after one or both parties has been married previously and their first mate still lives.
I will not try to address all the widespread ways of reasoning that arise when looking at this matter, but just mention a few. One is based on Matthew 5:32 and Matthew 19:9 where Jesus says "except for sexual immorality." These scriptures are often used to justify a divorce (and usually remarriage) if one of the partners has been unfaithful. There are many opinions about what is meant by "except for sexual immorality," often called "the exception clause." I believe it is a reference to the Jewish marriage customs. Bible scholars tell us that the Gospel of Matthew was written to Jews, and in the Jewish custom, the bride and groom were considered man and wife from the beginning of the betrothal period. The commitment was binding, but there was a year of preparation before the marriage was consummated and the two came together to live as one. If unfaithfulness (sexual immorality) was discovered during betrothal, the man was free to divorce his wife without further consequences. An example of this in scripture is Joseph and Mary (see Matthew 1:18-25). If a person does not accept the view that this exception applied only to the Jewish betrothal period, may I point out that while some may use this scripture to justify divorce on the basis of unfaithfulness, I do not believe there is any foundation for remarriage if we consider the scriptures as a whole.
Another common justification is the statement by Paul regarding all things becoming new in Christ. "Therefore, if anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new" (2 Corinthians 5:17). This is interpreted by some to mean that if a person is in an adulterous relationship (a second "marriage") when they come to the Lord, "all things are new" and the one they are with is their legitimate wife or husband from this point forward. If marriage were a Christian institution, perhaps this argument could have some validity. However, in the passages pertaining to marriage, there is no mention of faith before God being a factor. If a man and woman "leave and cleave," God considers them one whether they are Christians or not.
The Amplified Bible translation of this passage may help us: "Therefore if any person is [engrafted] in Christ (the Messiah) he is a new creation (a new creature altogether); the old [previous moral and spiritual condition] has passed away. Behold, the fresh and new has come!" (2 Corinthians 5:17, Amplified Bible) This brings out the truth that the "new creation" refers to the interior of a person, not his exterior circumstances, such as his marital situation.
Becoming a Christian is not an opportunity to get a new wife or husband, nor does a couple need to be married again because they were not Christians at their original ceremony. If a couple is in adultery when either or both turn to the Lord, the only way to be free from this sin is to repent and forsake the adulterous relationship. Yes, all things are new in the sense that I am now a new creation in Christ Jesus, but this does not make another person my wife or husband if they were not before.