“And the men of the area asked his wife (or about his wife), and he said, ‘she is my sister” (B’reishis 26:7). Just as Avraham had told the Egyptians, and then the people of G’rar, that his wife Sara was his sister (12:13 and 20:2), Yitzchok told the people of G’rar that his wife Rivka was his sister. Nevertheless, there were significant differences between the two. [It should be borne in mind that people were treated very differently then. This applies not only to the concept of slavery, gender differences, and how captives were treated, but also to how those who were mistreated were perceived. The willingness to risk a spouse being mistreated in order to avoid being killed takes on a different perspective when considering that there was not the same stigma attached to victims as there may be now. This concept deserves a much more in-depth treatment, but is not the focus of this piece. Nevertheless, when discussing Yitzchok (and Avraham) putting the virtue of their wives at risk in order to save their own lives, this point is important enough to mention, at least in passing.]
One of the main differences between Avraham presenting his wife as his sister and Yitzchok doing the same is that Avraham initiated the notion even before he came in contact with those he feared would kill him for her. Yitzchok, on the other hand, only said that she was his sister after he (or she, depending on how you read the verse, and there are commentators that read it both ways) was asked whether they were married. It is quite possible, even likely, that Yitzchok thought that the suffering endured by the people of G’rar on account of Sara being taken (see 20:17) would be enough of a deterrent that he didn’t need to present Rivka as his sister (see Midrash Lekach Tov and Midrash Seichel Tov on 26:7). However, upon seeing that they still asked about her, he realized that his life might still be in danger (“for he was afraid, saying, ‘lest the men of the area kill me over Rivka”), so followed the same game plan as his father (see Midrash HaGadol).
Another difference is that Avraham calling Sara his “sister” was much closer to the literal truth than Yitzchok calling Rivka his sister. After all, Sara was his brother’s daughter; just as his nephew Lot was accurately called his “brother” (14:14), Lot’s sister, his niece, could be called his “sister.” Rivka, on the other hand, while being Yitzchok’s blood relative too (his first cousin once removed), was much more distantly related to him than Sara was to Avraham. Nevertheless, if the term “brother” can be used to refer to a relative who is not part of the immediate family, the term “sister” can be used that way as well. It can be suggested that Yitzchok called Rivka his sister not only because it could be said to be literally true (by using the more liberal definition), but because doing so would be a not-so-subtle reminder about what had happened the last time a “sister” was taken by the leader of G’rar. And this seems to have worked, as this time the “sister” was not taken into anyone’s home. Rather, Avimelech waited to see whether Yitzchok treated Rivka as a spouse or as a relative (26:8), keeping his distance until he could verify what Rivka’s status really was.
Discussing Rashi’s comment (25:20) that Rivka was three years old when she got married, Rabbi Shimon Schwab cites several reasons why this is difficult to accept at face value. First of all, would a three year old be physically able to draw water for all of the men with Eliezer and their camels? How could the Torah call her a “na’ara,” a young maiden (24:16), a term used for a girl who is 12 years old, if she was much, much younger than that? And how could she be praised for her virtuosity (ibid) if the whole concept of being modest and virtuous doesn’t apply before the age of three?
Rabbi Schwab then quotes several sources (e.g. Midrash HaGadol and Seder Olam) who say explicitly that Rivka was 14 years old when she got married. He also references Y’feh To’ar’s commentary on Koheles Rabbah (7:3), who proves that she was 14 by subtracting Yaakov’s age when she died (98.5; he was 63 when he left home, spent 14 years hiding in the Yeshivos of Shem and Ever, worked for Lavan for 20 years, and was traveling for 1.5 years when Rivka died) from the age Rivka was when she died (133, the same age as K’has when he died, see Sh’mos 6:18 and Sifre, V’zos Hab’racha 357), meaning that she was 34.5 when Yaakov was born. Since Yaakov was born 20 years after Rivka and Yitzchok got married (see B’reishis 25:20 and 25:26), Rivka must have been 14.5 when she got married.
What, then, does Rashi mean when he says that Rivka was three? Rabbi Schwab quotes Rabbi Michoel Forshlager (a student of the Avnay Neizer; you can read a fascinating profile about him at http://jewishlife.com/news/print.php?ARTICLE_ID=35276), who says that when Rivka was born, she did not yet have the special, holy soul that would allow her to be Yitzchok’s mate and the mother of the Nation of Israel. Rather, in the merit of the “akeida,“ when Yitzchok was bound by Avraham to be slaughtered for G-d, this elevated soul entered her body. This occurred three years before Rivka got married, so she is described as being “three” when she got married, referring to how many years this holy soul was within her.
Rabbi Schwab takes this a step further, suggesting that it was actually Sara’s soul that entered Rivka after the “akeida,” as this was precisely when Sara had died (see Rashi on 23:2). He uses this to explain Rashi’s wording when Yitzchok brought Rivka into Sara’s tent (24:67); “behold she was his mother Sara,” meaning it was literally Sara, as it was Sara’s soul inside Rivka.
Based on this, we can add another dimension to Yitzchok saying that Rivka was “achoso,” which literally means “his sister.” Whether intentionally or through ru’ach ha’kodesh, Yitzchok was telling Avimelech and the rest of the men in G’rar that they better be careful, because the woman they were asking about was “achoso,” i.e. the same person (or at least the same soul) that his father had described as “achoso.” He was reminding them of their being afflicted when Sara was taken by Avimelech, and hinting to them that the same circumstances apply now as well; not only because he is Avraham’s son but because she is the “achoso” who brought punishment upon them the last time. By doing so, Yitzchok was hoping they would stay away from her. And, although it took some additional verification, they did.