Your post is a little hard to parse and I’m not completely sure what you are asking, but I’m thinking you are objecting to God’s (apparent) santioning of Abraham’s polygamy in contradiction to later laws forbidding it? If so, here’s my answer to that:
Try to get beyond the notion that the Bible relates events and history in the same way we would relate it. Just because we see people sinning in the Bible and God immediately striking them with lightning (as we might expect) doesn’t mean that God is condoning (or even tolerating) those sins. The Bible also isn’t the unsubtle morality play people make it out to be – you often have to read between the lines and see what ultimately results from the actions of the characters. Sometimes it takes a long time.
A good example of this is polygamy. People always ask, “If polygamy is bad, why doesn’t God condemn his servants or punish them when they engage in it?” Well, actually God punishes them by allowing the chips to fall where they may. In every case we read about bigamy and polygamy in the OT, something bad always happens as a direct result of it. It might take a long time sometimes, but you can easily trace it back if you take the time to do it.
Another example that constantly comes up is Abram’s actions in Egypt, where, to save his own skin, he tried to pass off Sarai as his literal sister, not mentioning that she was his wife… Well, after Pharoah found out he gave Abraham a bunch of gifts and sent him on his way? What’s wrong with that?
W-e-e-e-l-l-l, you might say that he consented to taking a little bit of Egypt with him when he left (much like the Israelites would do 500 years later, keeping Egypt in their hearts --it’s luxuries and idols – when they left). One of these gifts was a maidservant for Sarai, Hagar. What’s wrong with that?
We-e-l-l, it seems Sarah and Abraham got tired of waiting for God to make good on his promise of a son so they used Hagar to speed things up, Sarah nagged Abraham to produce a child with Hagar, the result of which was Ishmael. So what’s wrong with that?
We-e-l-l-l – As you know when the son of the promise (Isaac) did finally come along, Hagar and Ismael were cast out. Stinks for those two, but, ultimately, what is wrong with that?
W-e-e-el-l-l - as you also must know, the descendents of Ishmael went on to become traditional bitter enemies of Israel and caused them no end of death and trouble, especially when it came time for Israel to try to make their way to the Promised Land during the Exodus. It took a while, but what went around, came around.
Hope this helps.