It is just weird, really. Passing off your wife as your sister just doesn’t seem like the type of thing that the patriarchs of Judaism should be doing. And not only does it happen once in the Torah, it happens three times. Twice Abraham passes Sarah off as his sister [Genesis 12:10-20; 20:1-18] and once Isaac passes off Rebekah as his sister [Genesis 26:1-16].
The motivation for this rather odd act is fear. As Abram says to Sarai, “I know what a beautiful woman you are. If the Egyptians see you, and think, ‘She is his wife,’ they will kill me and let you live. Please say that you are my sister, that it may go well with me because of you, and that I may remain alive thanks to you” [Genesis 12:12-13].
Why are the patriarchs passing off their wives as their sisters? The explicit reason given in the text is fear for their own lives, but the deeper question remains of why the Torah includes such an unflattering portrayal of our patriarchs. A second and perhaps more challenging question is why the motif repeats itself three times.
The location of the stories in the Torah makes the question of motivation even more problematic. Each wife-as-sister scene occurs directly after God has made some pledge of prosperity to the patriarch. Right after receiving God’s pledge of safety, the patriarchs commit this rather scandalous act of weakness.
The traditional commentators differ (not surprisingly) as to the motives of the patriarchs. A famous midrash depicts how Abraham puts Sarah in a box and tries to smuggle her into Egypt. He then offers to pay any levy on the box until the customs officer became suspicious and opens the box discovering her. This midrash suggests that Abraham at least tried alternative plans before suggesting that she was his sister. Some commentators, such as Seforno, suggest that Abraham would be able to bide his time during the famine, make some money in the markets, and then leave Egypt with Sarah when the time was right.