In this week's Parsha, the Torah says, “Eileh Toldot Avraham; Avraham Holid Et Yitzchak,” "These are the children of Avraham, Avraham gave birth to Yitzchak." On this Pasuk, Rashi asks why the Pasuk repeats “Avraham Holid Et Yitzchak.” Wouldn't it be enough just to say “ViEileh Toldot Avraham”? Rashi answers that after Hashem changed Avraham's name, Yitzchak was born to emphasize Avraham's new name. Additionally, Rashi says that people were saying that Avimelech was the biological father of Yitzchak because when Sarah was living with Avraham she was not pregnant, but when she was with Avimelech for one night, the next Pasuk says that Sarah was pregnant. Therefore, in order to prevent people from making this claim, Hashem made Yitzchak look exactly like Avraham.
Two questions can be asked on this statement of Rashi. First of all, why are the Rabbis worried about the people who spread false rumors? Also, if Avraham had children before Yitzchak, and Sarah was the one who could not have children, then why does the Pasuk focus on Avraham and not Sarah?
In answering these questions, Rav Yosef Dov Halevi Soloveichik explains that a parent has a responsibility of raising a child and to pass down one’s values to the child. This is what Avraham was trying to do. He was trying to start the spread of monotheism in place of polytheism, something which he was trying to pass down to his son. However, some people felt this was impossible, and therefore, they said that Avimelech fathered Yitzchak, meaning that Avraham would not be able to fulfill his task, and the ideas that Avimelech believed in, polytheism, would stay with Yitzchak. In response, the Torah emphasizes “Avraham Holid Et Yitzchak,” that Avraham shaped the personality of Yitzchak, and that Avraham's ideas were passed down to him.
-Adapted from a Shiur given by Rabbi Yosef Adler at TABC.