When a famine occurs in the Land of Canaan, Yitzchak is forced to travel to Gerar. Similar to his father Avraham's experience years before, Yitzchak is about to face the challenge of having to say that Rivka is his sister rather than his wife. The immorality of the society of Gerar necessitated this decision, as Yitzchak feared for his life if he told the truth about Rivka. Immediately prior to entering Gerar, Hashem appears to Yitzchak and assures him that Hashem will bless him in the merit of Avraham. Hashem concludes this vision by highlighting the greatness of Avraham that warranted the blessings being bestowed upon his descendants. Avraham observed all the mitzvos of Hashem, which Chazal interpret to mean that he fulfilled the actual mitzvos of the Torah which he understood through ruach hakodesh even though they had not yet been given. Not only did Avraham observe the mitzvos of Hashem, but he is also described as "vayishmor mishmarti" - he was careful to safeguard these mitzvos. Rashi comments that this phrase refers to Avraham's fulfillment of even the rabbinic ordinations that were later instituted to protect the observance of Torah law. Examples of these are the many rabbinic prohibitions that we observe on Shabbos, thereby preventing desecration of Shabbos by Torah standards. Is there a reason that Hashem informs Yitzchak to be reminded that his father was one who safeguarded Hashem's mitzvos?
There are two interactions between Avimelech, the king of Gerar and Avraham that are recorded in Parshas Vayera. When Avraham hid Sarah's true identity as his wife because he feared that the people of Gerar would kill him, he was confronted by Avimelech who could not understand why he and his nation were being punished for his taking Sarah, being that he was not aware that she was Avraham's wife. Avimelech questioned Avraham's actions and Avraham responded that he had to act this way because there was no fear of Hashem in Gerar. Although Avimelech thought that he is not accountable for a sin done unintentionally, he is rebuked by Avraham that the background for such a sin is the lack of fear of Hashem in Avimelech's Kingdom. The Torah requires teshuva and atonement even for sins committed unintentionally. Perhaps one would have been more careful if one would have been more cognizant that Hashem is constantly watching. The rebuke that Avraham gave Avimelech for his unintentional sin is the correct response to Avimelech another confrontation between Avraham and Avimelech as well. When Avimelech came to Avraham to enter into a treaty with him, Avraham informed him that three wells had been stolen by Avimelech's servants. Avimelech defended himself by stating that he knew nothing about this. Once again, Avimelech is guilty for not being aware of something that he should have known about. As the king, he was responsible to prevent the crime of theft. Although he didn't know about this particular act, in a society in which the fear of Hashem doesn't exist the king is held accountable for fostering a climate in which these crimes occur.
Although Avimelech was not an intentional sinner, he fell short in his role of creating a culture of fear of Hashem, a heightened recognition of Hashem that would prevent these types of unintentional acts from occurring. Avimelech starkly contrasts with Avraham. Avraham is described as a "yerei Elokim" - one who fears Hashem - and the one who is "shomeir derech Hashem" - guarding the path of Hashem. Realizing the significance of observing Hashem's mitzvos, he not only observes them properly, but enacts proper safeguards to be certain that even unintentional violation of Hashem's word will not occur. It is this yiras Shomayim that is the basis for the safeguards enacted by Chazal to protect the mitzvos of the Torah. It is precisely when Yitzchak is about to encounter a culture very different from the one in which he grew up in when he is reminded of the legacy of his father. He must be careful in the land of Gerar not to be influenced by the place in which he found himself. Let us merit to learn from our avos how yiras Shamayim must be the central feature of our lives.
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