How could Avraham, the one who "spurns gifts," look forward to receiving royal wealth at Sara's expense? How does Avraham's conduct here correspond to his refusal to accept any spoils from Sedom?
Among the stories of Avraham told in Parashat Lekh-Lekha in his military victory over the four powers of the east and the celebration of his triumph in the city of Shalem (chapter 14). There the king of Sedom, the city that had been taken captive by the four kings and subsequently liberated by Avraham, offers Avraham all the spoils of Sedom he had retrieved, in exchange for the captives he rescued. But Avraham refuses to take as much as "a thread or a shoe strap" (14:23) from the spoils of Sedom. He explains, "so that you shall not say, 'It is I who made Avram rich'." However, Rav Yehoshua Katz, in his classic commentary on the Tur, known as "Derisha" (in Choshen Mishpat, 249), places Avraham's refusal to take the spoils within a broader context, viewing it as a fulfillment of the famous dictum, "Sonei matanot yichyeh" ("He who spurns gifts will live long" – Mishlei 15:27). Avraham turned down the king's offer because of the general value of refusing gifts.
As the Derisha himself notes, however, earlier in the parasha we indeed find that Avraham not only accepted gifts, but intentionally put himself in a situation where he would become wealthy by receiving gifts. As he and Sara left to Egypt to flee the famine in Canaan, Avraham feared that he might be killed so that his attractive wife would be available for marriage. He therefore asked Sara to pose as his sister, "that it may go well with me because of you" (12:13). Rashi explains this phrase to mean, "They will give me gifts." Avraham correctly anticipated that Sara would be abducted to the king's palace, and Avraham, as her brother, would be treated to royalty as a result. But how could Avraham, the one who "spurns gifts," look forward to receiving royal wealth at Sara's expense? How does Avraham's conduct here correspond to his refusal to accept any spoils from Sedom?
This difficulty led the Derisha and others to offer creative, alternative explanations of this verse. According to the Derisha, Avraham refers not to gifts he received from the royal treasury, but gifts he was given from other Egyptians who desired his wife. Suspecting that many Egyptians would compete for Sara, Avraham anticipated that the wealthier inhabitants would try to win his favor in an effort to convince him to give them his alleged sister. Avraham will therefore receive many bribes and become very wealthy. His wealth and stature will then help ensure Sara's protection from those who might seek to forcibly seize her. Avraham thus meant that by posing as his sister, Sara will bring about a situation where Avraham would become exceedingly wealthy and thus have the power to protect her. (In the end, of course, Pharaoh himself took Sara, and she was saved only by God's intervention.)
The Chid"a (Rav Chayim Yosef David Azulai, 18th century), in his "Penei David," offers a different explanation of this verse. He claims that Avraham refers here not to the gifts he receives when Sara is initially taken, but rather to the gifts given to him after God intervenes and forces Pharaoh to return her to her husband. Later, in Parashat Vayera, we read that in a similar situation, Avimelekh, the king of Gerar, gives Avraham and Sara generous financial compensation, which he described as "kesut einayim" – proof to the fact that he had not defiled Sara (see 20:16). The Chid"a suggests that the same occurred in Egypt, as well; after God's punishment of Pharaoh and his palace, the king went to great pains to guarantee Sara's protection from rumors. Anticipating all this as he makes his way towards Egypt, Avraham seeks to assuage Sara's fears by guaranteeing her that she would not be defiled. To the contrary, they will receive enormous gifts as part of an effort to protect her reputation.
The Moshav Zekeinim addresses this question, as well, and suggest a much simpler explanation, claiming that accepting the gifts was part of Avraham's disguise as Sara's brother. As brother of the woman desired by the Pharaoh, he would be expected to accept gifts and royal treasures. Had Avraham refused, he would have aroused suspicion, thus undermining his entire scheme. It turns out, then, that in Egypt, too, Avraham would have preferred to refuse the gifts, but he simply had no choice but to accept them.