ייִדישער מחשבֿה אויף ויקרא 21:20

The fundamental commandments that are not dependent on place, time, or any other factor are deeply rooted in the heart. They are the precepts, such as the charge that is entrusted to someone who is appointed to fulfill it. Therefore, King David said (Psalms 19:10), "The precepts of the Lord are upright, causing joy to the heart." These commandments were already known and weighed in the minds of the people before the giving of the Torah by the hand of Moses. They are numerous, like the Ten Commandments, except for the observance of the Sabbath, which was altered by Moses. Concerning these commandments, it is said (Genesis 26:5), "Because Abraham obeyed My voice and kept My charge, My commandments, My statutes, and My laws." If Jacob, our forefather, had known the prohibition of all incestuous relationships, he would not have married two sisters simultaneously. Therefore, it is stated (Leviticus 18:27), "For all these abominations, the people of the land who were before you have done, and the land became defiled." This includes engaging in same-sex relations, which is contrary to the will of God and is abhorred in its entirety. Similarly, engaging in intercourse with other kinds and bestiality are prohibited. Therefore, it is appropriate to interpret (Leviticus 20:17) "The near kinswoman" as referring to a person who has a close familial connection with his sister, who is the daughter of his father and mother. In the same manner, it is said (Exodus 14:30), "And Israel saw the Egyptians dead on the seashore." Consequently, Abraham said (Genesis 20:12), "Besides, she is truly my sister, my father's daughter, though not my mother's daughter." This serves as evidence that there is no punishment from the court for such cases. If one objects and asks why the prohibition is against the sister and not the brother, one might similarly ask why the distinction is made between a virgin and a non-virgin. However, this is not the proper legal argument to make in these cases.