The rabbis are mystified by the possibility that a man may marry a woman whom he hates (Deuteronomy 21:15). That a man would marry a woman he detests seems to be logically incongruous in that it is contrary to a man’s self interest. So the rabbis propose two solutions.
According to Rabbi Shimon in the Mekhilta, the Torah addresses reality. Polygyny is permitted. However, when a man marries two women, the inevitable result is that familial friction will lead to loving one wife and hating another. On this view, the law of primogeniture (i.e. endowing the firstborn son with a double share – regardless of the relationship between his mother and father) is also a caution against polygyny. That caution was taken seriously in that there is no recorded case of any rabbi in the Talmud with two wives.
Even though polygyny has fallen into desuetude (and remains illegal in Western society) Rabbi David Zvi Hoffman, writing at the beginning of the twentieth century, explains that the Torah offers us general guidance to avoid any action that might cause marital strife. He connects this scriptural passage with the previous one regarding taking a female captive (Deuteronomy 21:11). What motivates a man to take a female captive into his household is her beauty (eshet y’fat to’ar). Relationships that are built upon such petty factors are doomed to fail.
The Talmud (Yevamot 23a) offers a second solution. The word “hated” does not refer to the relationship between man and wife. Rather, it is a judgment of the marriage itself. There are some marriages that are valid though prohibited. For example, a kohen (priest) is forbidden to marry a divorcee. However, should he do so anyway, the marriage is recognized as valid. A man may not remarry his own divorced wife after she marries another man. But should he do so, the marriage is valid. Although the marriage may be valid, argue the rabbis of the Talmud, that relationship is hateful to God.
Today, readers are far more likely to understand the text to refer to a case where, over time, the initial loving relationship between husband and wife degenerates into differences so irreconcilable that enmity is unavoidable. Earlier rabbinic tradition, however, likely did not see this possibility as realistic. Or, even if they did, the rabbis were far more interested in idealizing marriage and preserving its integrity rather than considering its failure.