By holy example Abraham institutes multiple marriages under...
By holy example Abraham institutes multiple marriages under the condition that it is agreeable to the first wife and for the purpose of carrying out the command to reproduce in the case of a barren wife. The example also provides the possibility of marriage by purchase, since Hagar is said to be a handmaid of Sarah. She was not provided with a dowry. Although no new example is given in the Biblical story of Lot in Genesis nineteen, there are passages which can be misunderstood.
In verse eight, Lot offers his daughters to the men of Sodom in lawful marriage in his judgement against their attempted homosexual rape. In so doing he gives a positive injunction for marriage, rather than delivering his daughters up to degradation. In Genesis 19:31-38, the details show clearly that Lot did not accept incest. The fact that the daughters in the story give Lot wine to hide their plan indicates clearly that they knew their father would not agree to the arrangement.
In verses thirty-three and thirty-five the expression `he perceived not' shows that Lot is blameless. Thus the story does not condone such behavior. Nevertheless, assuming that legislation at the time of Lot was somewhat less than what we now possess, the actions of the daughters of Lot should not be judged on the basis of our greater knowledge. Their motivation was not degraded. It was a misguided attempt at obeying the basic command to reproduce.
The lesson of the experience is to show us to what lengths a human being can go when he depends on his own judgement or the judgement of other human beings in determining what is right and wrong. The story of the daughters of Lot confirms the need for divine guidance. Genesis 20:12 raises again the issue of incest, stating that Sarah and Abraham were children of the same father. This does not necessarily mean that they were from the same biological father.
It could very well mean that they were from the same ancestor on the father's side. In many cultures there is no distinction in terms between siblings and parallel cousins. The use of the word father in Semitic languages is very broad indeed. Two men are known to have been called the father of Abraham, and only one of them can have been his biological father. Terah is known from Genesis 11:27 et al., while Azar is known from the Qur'an 6:75 et al.
There is no reason to assume that Abraham and Sarah were biological siblings, whereas there is every reason to assume they were not.