‘Do not commit adultery” — the Seventh Commandment – is generally understood to mean that a married person should not have relations other than with his or her spouse. Thus it would seem that a man who has not halachically divorced his wife and takes another is breaking this commandment.

However, under Torah law, he is not, and that is why Israel Meir Kin remarried on March 20 without giving his wife Lonna Kin a get – the Jewish divorce document. The couple are civilly divorced but halachically they are not. If Mrs. Kin were to remarry, she would become an adulteress, but Mr. Kin will not be considered an adulterer by remarrying.

The reason is that the seventh commandment — lo tinaph, do not commit adultery – actually only applies to married women, and to men who have relations with them.

“Lo tinaph – ‘You shall not commit adultery’ – strictly speaking, this prohibition involves cohabiting with a married woman,” states the website of the Orthodox Union. “This is another of the Three Cardinal Sins, regarding which one must forfeit his life rather than violating.”

Many Jewish men in the Torah, including the patriarchs Abraham, Isaac and Jacob, have multiple wives, but no women do – so it is understood that as long as the man marries a woman who is single, it is not forbidden by the Seventh Commandment, even if he is married.

Rabbinic law is another matter. Having multiple wives has been prohibited by rabbinic law since the 11th century, when Rabbeinu Gershom, from France, issued a cherem — literally an excommunication but in this case a prohibition or injunction, stating that a man may only be married to one woman at a time. This has been Jewish law ever since, at least among Ashkenazi Jews.

So how did Mr. Kin get around this? Cherem is a post-biblical injunction, making it able to be countered by another post-biblical injunction. The injunction that counters cherem is something known as heter meah rabbanim – permission via the signatures of 100 rabbis. By getting signatures of 100 rabbis, Mr. Kin was allowed to remarry without giving a get.

But this rabbinic permission is not available for women, because a post-biblical law cannot override a law that is found in the Torah itself.

“There is no direct women’s parallel to the heter maeh rabbanim, because the latter cannot erase a Biblical injunction of adultery,” said Rabbi Yosef Kanefsky of B’nai David Judea, one of the rabbis who attended the protest against Mr. Kin’s remarriage in Las Vegas March 20. (See story, below.)

To some, the problem of agunot is an ironic one. Tanach and Gemarah teacher Ms. Atara Segal explained that men’s polygamy was originally meant for women’s and children’s benefit.

“This is a case where halacha is protecting the woman and the community,” Ms. Segal said. “If a woman has sex with more than one man we then don’t who the father is, whereas you always know whom the mother is.”

This ensures that children – and their whole community — know who their fathers are, and single women have a means of support. In ancient times a single woman, divorcee or widow would not have been able to support herself and her children without a husband.

“If there are more women than men, the women need to be able to marry someone, the men don’t,” Ms. Segal said. “It really is designed to protect a woman…A single man could earn a living and fend for himself. A single woman cannot earn a living and fend for herself.”

But that seems not to protect women like Lonna Kin or other agunot. Since Torah law cannot be changed – meaning that a heter meah rabbanim for women will not be possible — Rabbi Kanefsky said the only solution will be for Jewish marriages in the future to be conditioned on their promising to give a get if there’s a divorce down the road. This could be accomplished by pre-nuptial agreement.

“The best we can do for her (aside from annulment, which is a whole other topic) is what will be, I hope, the next generation pre-nup,” Rabbi Kanefsky wrote, “in which the man, at the time of the wedding, explicitly conditions his kiddushin (betrothal) upon his behaving properly at the time of divorce (should that time come).”

Related: Students trek to Las Vegas to protest wedding in agunah case