Polygamy OK?

You're right, the Bible doesn't seem to shame Old Testament patriarchs for having multiple wives. In fact, in Chronicles it actually seems to have been a blessing for a king to have many wives, probably because it multiplied his descendants. In Deuteronomy 17:17 Moses instructed kings not to multiply wives, but for purpose that the kings' hearts not be turned away. Probably, Moses meant that if kings multiplied foreign wives, in particular, that they might turn his heart toward idolatry (as later happened to Solomon [1 Kgs. 11:4]). In Leviticus 18:18 he forbid marrying multiple sisters, but seemed to indicate that the problem in breaking this law would have been rivalry between the sisters, not multiplicity of wives in general. The example of David, however, is not really that helpful. David was a man after God's own heart (1 Sam. 13:14; Acts 13:22), but he did many things that were not according to God's heart, i.e. he murdered Uriah the Hittite after committing adultery with Uriah's wife Bathsheba (2 Sam. 11; see esp. 2 Sam. 11:27).

Nevertheless, the Old Testament, and Moses' writings in particular, do not hold up polygamy as the ideal. Genesis is quite instructive in this regard. In the ancient Near East, creation narratives were used to demonstrate not just what was, but also what should be. It was generally understood and accepted that the world was created with purposeful order, and that to deviate from that order was sin. In writing the creation narrative of Genesis, Moses adopted this same perspective, and used the creation narrative to motivate Israel to return to the Eden, i.e. the Promised Land, in order to enjoy God's blessings in the restored creation. It was a real return to Eden. Jesus himself adopted this reading of Genesis, and with specific reference to marriage, in Matthew 19:1-9. There, Jesus argued that the law Moses had permitted regarding divorce was not the ideal. Rather, the ideal was the order God had established in creation. In the same way, the law permitted polygamy, but Genesis 1-3 demonstrates this was not the ideal toward which the people were to strive. The ideal was the model of creation: one man and one woman in a monogamous relationship. It is worth noting in this regard that the first polygamist mentioned in the Bible is the murderer Lamech (Gen. 4:19-24).

As Jesus indicated in Matthew 19, God did not always enact laws that perfectly represented his ideals. Rather, to some degree he accommodated his law to his people (compare Deut. 30:10-14). Even the New Testament contains no clear statement forbidding polygamy - though it also contains no record of extant polygamy, and lists monogamy as the ideal (1 Tim. 3:2; Tit. 1:6). This introduction of polygamy after the fall, and progression toward monogamy as we move toward the full restoration of God's kingdom, indicate that polygamy is not the ideal, and it is less and less permissible as kingdom of God progresses.