אמרי-נא אחתי את למען ייטב-לי בעבורך וחיתה נפשי בגללך
Please say that you are my sister, so that it will be good for me for your sake, and my life will be spared because of you
Due to a severe famine in the land of Canaan, Avraham and Sarah journeyed to the land of Egypt. Knowing full well the morality of such a place, Avraham was very concerned. His wife was tremendously beautiful, and if the Egyptians knew they were a married couple, they would have no problem killing Avraham and taking Sarah for themselves. However, if the couple represented themselves as siblings, they would be safe. The Egyptians would assume Avraham, as Sarah’s “brother,” was her protector, and could be persuaded to give her away in marriage.
Avraham asked Sarah to go along with this ruse so that it would be good for him. Rashi explains that Avraham expected that if they did this plan, they would give him lots of gifts, in order to persuade him.
How can we understand this? Avraham was afraid for their lives, and his mind was on monetary matters? Furthermore, we see later that Avraham was clearly not a greedy person. He refused spoils from war that were rightfully his. Why did Avraham express interest in receiving gifts through his ruse?
Our Sages tell us that there are three tremendous gifts that Hashem gave the Jewish people, and all of them are acquired with difficulty: Torah, the land of Israel, and the World to Come. They also taught that in the merit of the righteous women, the Jews were redeemed from Egypt. It is further taught in a Midrash that in the merit that Sarah came to Egypt and took precautions against immoral relations with the locals, her female descendants merited to take similar precautions.
Putting this all together, we can glean a deeper insight into Avraham’s intent. Avraham was telling Sarah that if they tell the Egyptians they’re married, they’ll simply kill him. If so, when they try to entice Sarah, it technically wouldn’t be “immoral” relations, as she would no longer be a married woman. Instead, he said to act as if they’re siblings. In that case, since they’ll definitely try their hardest to entice her, it will provide her tremendous reward. By taking whatever precautions she could to avoid being unfaithful to Avraham, it ensured that her descendants had the spiritual fortification to avoid immoral relations when they too were in Egypt.
In the merit that the Jewish women in Egypt retained their righteousness, due to the spiritual strength implanted into them by Sarah, the Jews merited to be freed from slavery. After the Exodus, they merited to three special gifts: Torah, the land of Israel, and subsequently the World to Come. When Avraham told Sarah that they would merit great gifts, he didn’t have in mind precious jewels, arrays of animals, or royal garments. Rather, his intent was for these spiritual gifts, assured to them by Hashem. Their ruse of the Egyptians planted the spiritual seeds necessary so that their descendants would gain eternity.
 Based on Nachalas Yaakov to Genesis 12:13, by Rav Yaakov of Lisa, the renowned Nesivos
 Genesis loc. cit.
 Ad. loc.
 Ibid 14:23
 For another approach to these questions, see Be’er Yosef to Genesis 12:13. An English translation is available at https://parshaponders.com/lech-lecha-5780/ and in the English adaptation of Be’er Yosef, available for purchase at https://mosaicapress.com/product/beer-yosef/
 Berachos 5a
 Sotah 11b
 Vayikra Rabbah 32:5
 I suppose the intent here (and of the Midrash loc. cit.) is the idea of “Spiritual DNA”, made famous by Rav Dessler in Michtav M’Eliyahu, where the forefather’s (and mothers) actions implanted in their descendants talents and abilities. For example, Avraham (and Yitzchak’s) willingness to give up their life for Hashem allowed Jews throughout the ages to die al kiddush Hashem. See also https://parshaponders.com/vayikra-5777/
 This approach doesn’t explain why Avraham said that it would “be good for me”, if the intent is for their mutual descendants