Incest Sometimes OK?
Why did God allow incest in the Bible with no clear punishment? How was it possible for Lot to become intoxicated two nights in a row and not know on either occasion that he was sinning with his daughters? And didn't Noah, his sons, and his sons' wives have to commit incest with their children as time passed?
Incest in the Bible is an interesting issue. In the beginning, incest was not only permissible but necessary. God created only two humans, Adam and Eve, and all other humans are their direct descendants. Thus, at least that first generation after Adam and Eve had to marry their full-blooded brothers or sisters. Once the first generation had reproduced, marriages could take place between brothers and sisters, between cousins, and between uncles/aunts and nieces/nephews.
When the flood occurred, this situation was repeated -- there was one senior couple (Noah and his wife), and there were three couples consisting of Noah's sons and their wives. Again, brothers and sisters probably married, as well as cousins, and uncles/aunts with their nieces/nephews.
Many significant and righteous biblical characters were married to close family members, such as righteous Seth who must have married his sister or perhaps a niece (Gen. 4:26; 5:3-8), and Abraham who married his half-sister (Gen. 20:12). Also, the parents of Moses, Aaron and Miriam were nephew and aunt (Exod. 6:20; Lev. 20:19; Num. 26:59). Such unions were later banned by the Law (Lev. 18:9-14; Lev. 20:17,19).
The specific biblical commands against incest do not appear until the time of the Mosaic Law. Prior to that time, these relationships do not appear to have been condemned explicitly. In the Mosaic Law, it is interesting to note that when incest is prohibited, it appears to be prohibited on the basis of unchanging moral principles (some of the commands contain such qualifications as "it is your father's nakedness" [cf. Gen. 9:22ff.]).
This leaves us with an ambiguous view toward incest in the Bible. At some point prior to the Mosaic Law, it was implicitly commanded by God (e.g. Gen. 1:28), and therefore could not have been sinful. In the Mosaic Law, however, it takes on a sinful moral quality. As we seek to reconcile these facts, we cannot do violence to either set of historical facts. One option is to interpret the Mosaic Law as forbidding incest not on the basis of unchanging moral principles, but on the basis of changing moral principles (e.g. culturally, socially, religiously, or otherwise conditioned principles).
An important factor to consider as we struggle with this is that the original audience of the Pentateuch (Genesis through Deuteronomy) lived in Moses' time. Moses did not write the Pentateuch simply to teach what happened in prior history. Rather, he had very specific goals for his writings to accomplish that were tied very closely to his mission as the leader of God's people in the Exodus. Moses did not think it important to explain in writing why incest had not been forbidden in the past. He felt it was enough for his audience to understand God's requirements for them.
Notice in this regard that Moses records very few of the laws which God placed on man during the primeval and patriarchal times, though he clearly assumes such laws existed. For example, he clearly assumes it was wrong for Cain to kill Abel, as well as that these brothers both knew the requirements for proper sacrifice to God, but Moses nowhere records how they knew these things.
In point of fact, Moses leaves us with many unanswered questions and unreconciled tensions. This should not, however, disturb our faith any more than it should have disturbed that of Moses' original audience. They knew enough to understand what God required of them, and to understand how to glorify him in their marriages. For us, the question is somewhat more difficult: not knowing precisely why God commanded what he commanded in the Mosaic Law increases the difficulty of knowing how to apply those Laws in our own time. I would suggest that we take our cue from Moses' apparent argument from unchanging moral principles and hold the same standards today.
Regarding the possibility of how Lot could have not known that he had slept with his own daughters, I'm afraid I have no firsthand knowledge of such extreme drunkenness. However, I think it is reasonable to believe that given the proper pharmacological influence, some people are capable of such unwitting behavior. That this is unlikely, however, may be part of the point of the story. The reason this account is included in Genesis 19 is to explain to Moses' original readers (Israel during the Exodus) their relationship to the nations of Moab and Ammon which bordered the Promised Land. On the one hand, Moses wanted his people to understand that these people were cousins of the Israelites, and so were not to be annihilated. On the other hand, he wanted to mock Moab and Ammon so that the Israelites would not fear them. If indeed it is rare to be so unaware when drunk, this would add to the insult against Lot, and thus increase the mockery of Moab and Ammon.
We have no evidence that parent-child incest was ever acceptable, and no evidence that what Lot's daughters did was not condemnable even prior to the Mosaic Law. We also do not know that God did not judge Lot or his daughters in some way for their actions. In all events, we can be assured that God's justice prevailed (Rom. 9:14), but we cannot know precisely how it prevailed, or by what standard it was measured (ultimately the standard is God himself; but we are unaware of any specific stipulation that Lot would have known to keep).
In summary, though the Bible leaves us with many mysteries and unanswered questions, I think it does give us sufficient information about how we are to understand our relationship with him now, and how we are to obey him now. As we apply the Law to our lives today, however, it requires great wisdom for us to know how to do so properly.
Answer by Ra McLaughlin