There is an excellent article on the matter of polygamy here by Bishop Glenn Davies from Sydney - Is Polygamy a Sin? He makes this comment:
While it is true that legislation existed under Mosaic Law to regulate polygam(Exodus 21:10-11), such legislation did not thereby legitimise polygamy. Rather it is akin to the sufferance exercised by God, a divine permission, which best explains the accounts of polygamy in the Old Testament.Serena's question however related rather to the felt imbalance: on the one hand, men were allowed this polygamous lifestyle; on the other, those accused of adultery were usually wives rather than husbands. I think the right responses is to say that, as Davies suggests, polygamy is conceded rather than endorsed; that it is a sign of wealth and power rather than a social norm, or seen as a sexual liberterianism of a kind; and that as such it still involved vows and contractual agreements that needed to be honoured...anything else?
To take it further: is the OT unacceptably patriachal? Does the whole approach to polygamy/adultery indicate that the status given to women was somehow offensive to our contemporary sensibilities? Is violence against women not condemned as it should be? Here are a few points in reply:
1. Women share co-humanity with men. Genesis 1 and 2, quite remarkably for their times, assert the full participation of women in the image of God and the flesh of Adam. She is not a lesser being, or a being of a different nature. She stands side by side with Adam.
2. Women are given a voice. One complaint from feminist interpreters is that women are largely silent in the Bible's narrative. But this would be to neglect the Songs of Miriam, Deborah and Hannah in which they are certainly given a voice. The Song of Songs seems to be largely narrated by a female voice - and gives startling (if we are expecting to see patriarchalism everywhere) expression to female sexual desire. God frequently uses women rather than men to show his subversion of men's determination to sort it out for themselves.
3. If women are significant in terms of their roles as wives, mothers, daughters and so on, it is worth saying that the individualism we now value so highly was not a part of the cultural context of the Bible. It is true of men as well that they were fathers, brothers and sons as much as individuals. Sins against individuals had ramifications for their families.
4. The law actually seeks to protect women as vulnerable to abuse by men. It also takes the actions of women just as seriously as men in that they are held responsible for their sin as well.
5. In Leviticus it is true that menstruation leads to a state of ritual uncleanness which needs purification. But it is also true that any male emission leads to the same uncleanness. Note that this does not mean 'sinfulness', by the way. It is a symbolic reminder of the human inability to remain holy.
It helps to remember that, in the OT, there are laws and customs given that are particular to the time and place: not everything should be held as a universal affirmation that this is the right course of action for all times and places. Remember that the OT points ahead to something greater - the need for something more definitive and lasting if the promises of God are to be fulfilled.
