Genesis 20:12Meaning & Commentary from the Church Fathers

In an attempt to defend himself, the patriarch stated, "Do not assume that I have deceived you in this instance: she is indeed my sister; she is my father's child, though not my mother's child; and she has become my spouse. I claim that she and I share the same father, which is why I refer to her as my sister. Thus, do not judge me harshly; the dread of death compelled me to act as I did, for I feared that you might kill me because of her and take her for yourselves. Even in this situation, my words were not untrue."

Abraham responded by saying, “I was fearful, which is why I referred to Sarah as my sister; I did not speak falsely, for she is truly my sister, my father’s daughter, although not my mother’s daughter. In relation to me, she is my father’s sister because she is the daughter of my father’s brother. However, she is not my mother’s sister, since Haran, the son of Terah, did not take a sister as his wife, but instead chose a stranger. She, valuing her own lineage, chose to stay within her own tribe and did not wish to accompany her son Lot or her daughters Sarah and Milcah.”

She is the daughter of his brother Aran, not his sister. However, the Hebrew text states, "She is indeed my sister, the daughter of my father, but not the daughter of my mother," which suggests that she was likely Abraham's sister. In his defense, we assert that at that time, such unions were not yet prohibited by law.

Indeed, a sister. (Gen. 11:29) Some interpret the phrase "My father's daughter, but not my mother's daughter" to mean that Arran was not born of the same mother as Abraham. Others suggest more straightforwardly that Sarah was the child of Farrah, differing in maternal lineage from Abraham. The potential threat of being assimilated among the Gentiles may have prompted a devout household to such lengths as to engage in these unions. Nevertheless, the weight of natural law against incest influenced not only Abraham but also the Canaanites. This is shown by the fact that through referring to his wife as a sister, he aimed to disguise their marriage from them. Moreover, when he mentioned his marriage to his sister, he quickly followed with a justification for this union, asserting that she was not my mother's daughter.