John Gill's Exposition of the Whole Bible
Genesis 11:29
And Abram and Nahor took them wives,.... Very probably after the death of their elder brother Haran, whose daughters they married, at least one of them did, and some think both;
the name of Abraham's wife was Sarai: it is not said whose daughter she was, unless she is the same with Iscah, the daughter of Haran, and so had two names, Iscah her name before marriage, Sarai after it, Abram calling her "my mistress", as "Sarai" signifies, as she called him my lord: so the Targum of Jonathan, Iscah, this is Sarai; in like manner Jarchi, Baal Hatturim, and other Jewish writers f, take them to be the same; but according to Genesis 20:12 Sarai should be the daughter of Terah, the father of Abraham, by another woman; and so the Arabic writers g say,
"the mother of Abraham died, whose name was Juna; and Terah married another wife, whose name was Lahazib; she bore him Sarah, whom Abraham afterwards married:''
[and] the name of Nahor's wife Milcah, the daughter of Haran, the father of Milcah, and the father of Iscah: so that Nahor married his brother's daughter, which sort of marriage was then allowed of, as formerly that of own brothers and sisters, but afterwards was strictly forbidden in the Levitical law: this account is given of Nahor's wife, as Aben Ezra observes, to show the pedigree of Rebekah, Rachel, and Leah: some think, as before observed, that Abram married the other daughter of his brother Haran, Iscah, and that she is the same with Sarai; and indeed, without supposing that, it is difficult to conceive for what reason this should be observed, that Haran, the father of Milcah, was also the father of Iscah; and if Sarai is not Iscah, no account is given by Moses of her descent, which may seem strange; and it can hardly be thought he would omit it, when it must be so agreeable to his people to know from whom they descended, both by the father's and mother's side.
f Bereshit Rabba, sect. 38. fol. 33. 3. 4. g Ut supra, (Elmacinus, p. 31. Patricides, p. 17.) apud Hottinger. p. 281.