In this week's parsha, the Torah says, "And the sons of Yaakov came in from the field when they heard; and the men grieved, and they were very wrought, because he had wrought a vile deed in Israel in sleeping with Yaakov's daughter; and so ought not be done," (לד:ז). The obvious question here is, once the Torah has stated that he had done a vile thing, what need is there to say he ought not to have done so. This seems unnecessary. Rashi appears to answer that the Pasuk emphasizes that Shechem, who slept with Yaakov's daughter, committed two violations. The first one is of Hashem's law regarding licentious relationships, and the second one is a law which the people of the land themselves adopted after the great flood. The people who adopted this code of behavior did so, because they understood its necessity on their own. This teaches a very important lesson, that decent people intuitively respect Hashem and his Torah, and even if they cannot articulate the reason for it, they still follow Him. They may have forgotten the reason for the original source of the law - God's command - because it was already twelve generations after the Mabul. Perhaps this explains why the law was violated. It is insufficient to adhere to a law because of a societal convention. The motivation must be to keep God's eternal laws, because societal convention is open to change and, unfortunately, deterioration. This should serve as a lesson to keep in our minds, that we keep the Torah not because our family does, but because God commanded us to do so.