Christ teaches us in the Sermon on the Mount that marriage is sacred. If a man pursues a married woman with the intent to defile her current marriage then he’s as good as done it: wrongful intent is equivalent to wrongful action. (Mt 5:27:28) It’s about the heart, not just the action.
In the process, Jesus teaches us something else about marriage: when God’s Law permits divorce (31), the spirit of the marriage relationship implies the grounds for divorce are quite strict. Note carefully the qualifying exception: sexual impurity or infidelity (32a); it’s when a husband has come to hate, resent or mistrust his wife in a manner comparable to what’s expected if she’s become sexually impure, that we should consider the relationship properly irreconcilable. (Mt 1:18-19)
This can easily be seen in the Torah itself: it’s when a wife finds no favor at all in her husband’s eyes that he’s to divorce her. (De 24:1) If his heart has become so hard towards his wife that he finds no mercy or compassion for her, no love or concern or care for her, the spirit of the marriage is already broken so deeply that it’s better for the woman to be released of the marriage bond. Divorce isn’t God’s original intent for marriage; it’s how Love deals with hardness of heart. (Mt 19:8)
The implication is that reasonable men don’t become so hardened toward their wives, such that they cannot possibly live with them in peace. So, as long as people are minimally reasonable, there should be no divorce … as long as wives aren’t adulterous.
However, the Pharisees had evidently turned this provision for divorce under exceptional circumstances into a sort of wife-swapping, putting away their wives for trivial reasons and deeply violating the spirit of the marriage covenant. (Mt 19:3) In these cases, where the marital relationship isn’t so deeply broken, marrying a divorced woman permanently breaks the marriage covenant in much the same way adultery does (Mt 5:32a), because this step prevents her from being reconciled to her former husband according to God’s Law. (De 24:3-4)
We should keep this context in mind when Christ adds: “and whosoever shall marry her that is divorced committeth adultery.” (32b) This is significant since in Torah, when a woman is divorced by her husband she is free to remarry. (De 24:2) Is Christ saying Torah permits a certain kind of adultery? Is He changing the moral standard?
Paul doesn’t seem to think so: he says if an unbelieving man departs his marriage, implying he abandons or divorces his wife, she’s no longer bound to her marriage covenant, implying she’s free to remarry (1Co 7:15), just as Torah says. Paul wouldn’t allow this if remarriage was inappropriate in a properly irreconcilable context, if it constituted adultery under a newer, higher standard set by Christ.
It seems much more reasonable to interpret Christ, not as correcting Torah or creating a higher standard, but focusing on the spirit of marriage. Re-marrying a divorced woman under less severe circumstances, unless all reasonable hope of the prior marriage being reconciled has expired, expresses an irreverence for the marriage covenant.
Divorce is acceptable only under the most extreme relational circumstances, and the divorcing husband should consider his action permanent. If a divorced woman believes her former husband may eventually change his mind, and wants to wait and leave the door open for reconciliation, that’s up to her; it isn’t necessarily wrong for her to move on, but if she does she’s effectively permanently sealing the termination of that marriage, as her former husband has decreed it.