אִמְרִי־נָ֖א אֲחֹ֣תִי אָ֑תְּ לְמַ֙עַן֙ יִֽיטַב־לִ֣י בַעֲבוּרֵ֔ךְ וְחָיְתָ֥ה נַפְשִׁ֖י בִּגְלָלֵֽךְ׃
Sabihin mo, pakiusap, na ikaw ay aking kapatid; upang ako'y makinabang dahil sa iyo, at ang aking buhay ay maligtas dahil sa iyo.
Rashi
למען ייטב לי בעבורך THAT IT MAY BE WELL WITH ME FOR THY SAKE — they may give me presents.
Chizkuni
אמרי נא אחותי את, “please say that you are my sister.” Avraham reasoned that if the Egyptians were to ask him if Sarai was a married woman, he would respond by claiming that her husband had abandoned her. The Egyptians would therefore have no reason to kill him on account of her absent husband, and they would leave her alone.
Sforno
למען ייטב לי, so that when you will say that you are my sister, each one will entertain the hope that I will agree to your marrying them. Therefore, none of them will have any reason to kill me. Rather, he will seek my approval by offering me a dowry for you. It was the custom in those days that the father of the bride would be bribed with money or its equivalent to agree to let his daughter marry someone. This also explains why the Torah speaks of מהר ימהרנה in Exodus 22,15-16, i.e. “he (the seducer) shall pay a heavy dowry,” and why the option to refuse such a marriage is not so much the girl’s but her father’s, as we see from the verse following.