Nahum Sarna

We read in class a commentary by Nahum Sarna which explains Yaakov's behavior. We see that Yaakov bought the Bchorah from his brother. Sarna explains that in ancient times, this was not an unheard of practice. In ancient Near East societies, there was a legal precedent for Yaakov's actions. But Yaakov was still punished for his actions. Why?

Yaakov was punished because there was really something else wrong with this whole situation. Despite the fact that it was legally okay, what Yaakov did was morally and ethically wrong. He, as an ethical monotheist and as a proponent of tzedek and mishpat, should have known better. Even though it can be argued that this was a necessary step, the way he went about it was not right. Because of this, he was plagued by many problems in his future.