Here is a quote from Timothy Keller where he deals with the hard subject of Polygamy and Primogeniture (the oldest son got everything) in the book of Genesis. Over the years, many women in particular have asked me why God would allow polygamy, and seemingly bless it. Keller makes it so clear that the Lord was actually working against it throughout his redemptive history with mankind. Here is the quote below.

Many years ago, when I first started reading the Book of Genesis, it was very upsetting to me. Here are all these spiritual heroes—Abraham, Isaac, Jacob, and Joseph—and look at how they treat women. They engage in polygamy, and they buy and sell their wives. It was awful to read their stories at times. But then I read Robert Alter's The Art of Biblical Narrative. Alter is a Jewish scholar at Berkeley whose expertise is ancient Jewish literature. In his book he says there are two institutions present in the Book of Genesis that were universal in ancient cultures: polygamy and primogeniture. Polygamy said a husband could have multiple wives, and primogeniture said the oldest son got everything—all the power, all the money. In other words, the oldest son basically ruled over everyone else in the family. Alter points out that when you read the Book of Genesis, you'll see two things. First of all, in every generation polygamy wreaks havoc. Having multiple wives is an absolute disaster—socially, culturally, spiritually, emotionally, psychologically, and relationally. Second, when it comes to primogeniture, in every generation God favors the younger son over the older. He favors Abel, not Cain; Isaac, not Ishmael; Jacob, not Esau. Alter says that you begin to realize what the Book of Genesis is doing—it is subverting, not supporting, those ancient institutions at every turn.

When I read Alter's book, I then reread the Book of Genesis and loved it. And then it hit me: What if when I was younger, I had abandoned my trust in the Bible because of these accounts in Genesis? What if I had drop-kicked the Bible and the Christian faith, missing out on a personal relationship with Christ—all because I couldn't understand the behavior of the patriarchs? The lesson is simple: Be patient with the text. Consider the possibility that it might not be teaching what you think it's teaching.

Tim Keller, in the sermon "Literalism" (available on PreachingToday.com on 5-17-10)