The Torah has a special word for interventions on someone else’s behalf: chesed. Though chesed is commonly understood to mean “kindness,” in the Torah, the meaning is more clinical: “acting on someone else’s behalf.”
So, for example: Lot describes the angelic deliverance from Sodom as a chesed, and the Torah tells us that the search for Rivkah, Isaac’s wife-to-be, was full of acts of chesed, of divine intervention. So, too, G-d intervenes, acts with chesed, to promote Joseph when in prison – and Joseph asks the grateful butler to repay him with chesed by mentioning Joseph to Pharaoh. Jacob asks Joseph to interrupt the normal way of treating the dead, and to “do me the chesed” of not burying Jacob in Egypt. Moses praises G-d as acting with chesed, divine intervention, to all the descendants of our forefathers, as well as forgiving the people their iniquity.
This is really quite specific. All of the above are actions that did not have to happen – that, had the normal course of events followed, would indeed not have happened.
Avram and Sarai have an early example of this word in action: “I thought,” said Abraham, “Surely there is no fear of God in this place, and they will kill me because of my wife. And besides, she is in truth my sister, my father’s daughter though not my mother’s; and she became my wife. So when God made me wander from my father’s house, I said to her, ‘Let this be the chesed that you shall do me: whatever place we come to, say there of me: He is my brother.’” (Gen. 20:11-13)
Which is really quite specific, when one considers that the laws against incest mysteriously use the word chesed for a forbidden relationship: but only between siblings.
If a man marries his sister, the daughter of either his father or his mother, so that he sees her nakedness and she sees his nakedness, it is a chesed; they shall be excommunicated. (Lev. 20:17)
How is incest a chesed?
The answer is in the text. Revisit the examples: G-d intervenes to save Lot from Sodom. But in hindsight, it is a failure: Lot later commits incest, and permanently separates from G-d and Avraham.
Saving Lot was a good idea, rooted in good intentions. But the end-result was a failure.
Similarly, Avraham asks Sarai to lie for him. But he did not need to do this! After all, once the men who took Sarai learned that she was married, they did not kill Avraham to possess her – his positive intentions turned into bad results.
We should not sugarcoat this: Avraham and Sarah suffer greatly from her telling powerful men that she was Avraham’s sister. She is taken into other men’s harems, and her marriage is subsequently marred with harsh words, jealousy, and unhappiness. When Sarah dies, she does so away from her husband, telling us that Avraham and Sarah had in fact separated from each other sometime before her life ended. The requested chesed, intervention, clearly led to marital damage.
Joseph’s request to the Butler, also rooted in good intentions, also fails. The Butler does not do as Joseph asked. Joseph’s redemption is delayed.
Which means that we can now understand why sibling incest is called a chesed: It seems like a good idea at the time. After all, how much easier would a marriage be if it is between two people with practically everything in common – family, traditions, culture, etc.! Indeed, siblings in principle have much less opportunity for conflict. And – bonus! – there would be no in-laws!
And yet.
So the Torah is telling us that marrying one’s sister would be like Sarai lying to save Avraham’s life, or G-d delivering Lot from Sodom: Despite seeming like a good idea at the time, it won’t work out that way.
Nevertheless, the above explains why the Torah specifically calls sibling incest chesed, using the very same language that Avram used to describe his relationship with Sarai: Sometimes the very best intentions can still lead to bad outcomes.
P.S. Not all acts of chesed fail, of course: burying Jacob in Israel, and the G-d’s chesed to the Jewish people both worked out in the end. At least I like to think so.
Creativejudaism.org