1) When approaching Egypt, Avraham asked Sorah to pretend to be his sister so that the Egyptians won’t kill him in order to marry her (12:12-13). Of what assistance would this plan have been, as it would have served to spare Avraham’s life, but it would have resulted in the married Sorah engaging in forbidden relations?
The Hakesav V’Hakabolah cites the Rambam (Hilchos Ishus 1:1), who explains that before the Torah was given, divorce didn’t require a legal procedure, and when a couple separated with the intention of no longer being married, they were legally divorced. As such, he suggests that in asking Sorah to say that she was his sister, Avraham was telling her to mentally declare that she was like his sister and was no longer his wife, in which case she wouldn’t be engaging in forbidden relations.
Rav Chaim Kanievsky in Tama Dekra explains that Avraham was relying on the fact that if any Egyptian wished to marry Sorah, he could insist on such a large amount of gifts that nobody would be able to meet his demands, and there was no practical concern that she would be forced into forbidden relations. He could only do this if the Egyptians viewed him as Sorah’s brother, because if they knew that he was her husband, they would realize that the only way to marry Sorah was to kill him. He adds that Avraham’s mistake was that it didn’t occur to him that Pharaoh himself, who could meet Avraham’s monetary demands, may be interested her, thereby negating his entire plan.
The Mishmeres Ariel cites the Gemara in Nedorim (91b) which teaches that a person’s evil inclination has a stronger desire for a married woman, who is forbidden to him, than for a single woman. By claiming to be siblings instead of spouses, Avraham was hoping that the Egyptians would no longer be as interested in Sorah if they believed that she was unmarried. (R’ Ozer Alport)
2) The Pirkei D’Rebbi Eliezer 29) writes that Avraham Avinu’s bris took place on Yom Kippur. Avraham Avinu kept the entire Torah, and the halachah is that only a bris which is bizmanoi [on the eighth day] overrides Shabbos. Since Avraham’s bris was shelo bizmanoi [not on the eighth day] how was he allowed to it on Yom Kippur?
