What the texts of the Bible reveal is a gradual evolution toward an appreciation of the value of marriage as an equal and lifelong partnership between a man and a woman. Our understanding of marriage has evolved even within our own lifetime and over centuries it has evolved considerably.
The Old Testament indicates that the polygamy was practiced by Abraham, Isaac and Jacob, as it has been by many nomadic peoples, particularly in ancient times. In these patriarchal societies the husband was chief of the family tribe and wives were purchased from another patriarch. While the stories of Abraham and Sarah and Jacob and Rachel indicate that love might be a part of such relationships, women were also treated as possessions, as we read of in the story of Abram giving his wife to Pharoah to ensure his own safety (Genesis 12:0-16).
While the practice of polygamy held some advantages for nomadic tribes (where infant mortality was high and many children were essential to maintaining the family enterprise) the Old Testament stories also hint at the disadvantages: the lobbying for positions of influence, the internal jealousies, and the tensions over who was entitled to the birthright ensured by the patriarch’s blessing. David and Solomon are also described as having many wives, but such households would have been enormously expensive to maintain, and created a palace brimming with interfamilial intrigue. Old Testament descriptions of polygamous relationships cease after the time of Solomon. Perhaps common sense and experience were the means by which God led people to an awareness that monagamy worked best as a way of ensuring an equal, faithful, and loving relationship between husband and wife.
The book of Genesis, even as it describes the polygamy of the patriarchs, relates in its creation stories a view of the relationship of man to woman that provides a basis for monagamous marriage. The human person is described as being in the Divine image precisely as male and female (Genesis 1: 27). Woman is also described as a “suitable partner” for man (Genesis 2:18), indicating a relationship of equals. The woman is described by the man as “bone of my bones, and flesh of my flesh”, evidence of an intimate relationship based in love (Genesis 2:23). The story concludes that “the two of them become one body” (Genesis 2:24), describing a relationship that is unique and permanent. Jesus prohibited divorce (permitted in Mosaic law, although it was far easier in his time for a husband to divorce his wife than for a wife to divorce her husband) in order that couples might mirror the relationship of faithful intimacy and love that Genesis described in the creation passages (Matthew 5:31-32). Catholics consider marriage a “sacrament” because its unconditional promise of two people to each other, “for better or for worse, until death do us part” provides an image of the faithful, loving relationship that God wants to have with every person.