Genesis and the Law of Moses

Genesis is situated before four books of the Law, all of which were believed to be written by Moses by most people until the past couple of centuries. I believe that Genesis provides us a background for the books of the Law, showing us in part why the Law was needed.

Genesis is filled with Laws of Moses that were broken or obeyed.  For example, in the very early chapters of Genesis we are given a story about how Moses' Law, which said, "Thou shalt not murder," was broken. Later in Genesis, Joseph's brothers almost killed their own brother, but decided last minute to sell him into slavery instead, which broke another of Moses' Law which condemned kidnappers to death.

There are other stories as well that spell out other broken Laws. Here are just a few examples:

REDEMPTION

If two brothers are living together on the same property and one of them dies without a son, his widow may not be married to anyone from outside the family. Instead, her husband’s brother should marry her and have intercourse with her to fulfill the duties of a brother-in-law. The first son she bears to him will be considered the son of the dead brother, so that his name will not be forgotten in Israel. (Deuteronomy 25:5-6)

When Reuben's son (Er) died, Er's brother was suppose to have sex with the widow in order to insure that Er's name would continue, and to give the widow a child to take care of her in her old age. Reuben's son did not fulfil his end of the bargain, and so the Lord slew him. It was only through the widow's (Tamar) deceit and cleverness that she was able to get the child she wanted, thus fulfilling a Law that was not yet in existence.

TREATMENT OF THE FIRSTBORN

If a man have two wives, one beloved, and another hated, and they have born him children, both the beloved and the hated; and the firstborn son be hers that was hated: then it shall be, when he maketh his sons to inherit that which he hath, that he may not make the son of the beloved firstborn before the son of the hated, which is indeed the firstborn. (Deuteronomy 21:15-16)

The whole reason Reuben had sex with his mother-in-law was a reaction to finding out that he was not getting the first born honor... and in the end he did not receive the inheritance or the honor of the first born.

TREATMENT OF STRANGERS

And if a stranger dwells with you in your land, you shall not mistreat him. The stranger who dwells among you shall be to you as one born among you, and you shall love him as yourself; for you were strangers in the land of Egypt: I am the LORD your God. (Leviticus 19:33-34)

There are several places in Genesis where strangers are either treated well (Abraham and Lot) or treated poorly (Sodom).

INCEST

Many different incestial relationships are forbidden in Leviticus 18, 20 and in Deuteronomy.  These  relationships of incest were abominations and some of the reasons God destroyed nations that lived in the promised land (Leviticus 18:24-30).
Here are some of the forbidden relationships found in Genesis:
1.   Abraham married his half sister Sarah.
2.   Lot's daughters had sex with their father.
3.  Tamar slept with her father-in-law.
4.   Reuben slept with his step mom.

I think it may be that by the time Moses' Law was written, people were changing their values.  In Genesis times it was common and acceptable to do anything in order to have children.  Having children was more important than avoiding incest.

Secondly, because Abraham had come from a nomadic family and continued to wander, marriage in his tribe tended to be in the family.  They didn't build long term relationships with the locals, so they did not trust them; and because they didn't trust them, it was only natural to marry inside the family.  

By the time the Law was written, Israel was no longer nomadic, Israel's culture had changed so there were literally thousands of partners to choose from in one's own tribe.  Incest was no longer needed and its popularity was waning. 

These are the stories from Genesis that come to mind.  I suppose there are others, anybody know of any?