And yet indeed she is my sister— It appears as plain as words can make it from this verse, that Sarah was indeed the sister of Abraham, born of a different mother, but of the same father: and one would wonder whence it comes to pass, that some expositors are so industrious to justify an opinion which this verse so plainly contradicts, that Sarah is the same person with Ischah, the daughter of Haran, mentioned ch. Genesis 11:29. Abraham is dealing here with Abimelech in the fairest and openest manner, and justifying himself as far as he could: but what justification would it be, to say Sarah is indeed, as I have called her, my sister, i.e.. my near relation, the daughter of my brother Haran? It is to be remembered, that he says she is the daughter of my father, not of my mother, to shew the lawful-ness of his marriage with her, which was allowed in those times with sisters by the father's side, but not with uterine sisters.
Related Commentaries of Genesis 20:12
Genesis 20:12
12 And yet indeed she is my sister; she is the daughter of my father, but not the daughter of my mother; and she became my wife.