In the last Pesukim of Perek 34, Yaakov reprimands Shimon and Levi for murdering the inhabitants of Shechem. He says, "You have discomposed me, making me hated among the inhabitants of the land...I am few in number and should they band together and attack me, I will be annihilated ‑ I and my household." They answer, "Should he treat our sister like a harlot?" Following this response, there is a Parsha break, and the Torah addresses another topic, that of Yaakov's leaving Beth‑El.
Why did Yaakov reprimand his sons for murdering the inhabitants of Shechem when in fact Shechem did treat Dina, their sister, "like a harlot?" And what is the rational behind his anger?
Before one can understand Yaakov's response and his sons' responses to him, one has to understand how they understood the sin against Dina.
According to Shimon and Levi, if a group of men from a nation commit a sin, it is as if their entire nation committed the sin with them. Thus, when Shechem treated Dina improperly, the entire Nation of Shechem had to be punished.
Yaakov, on the other hand, had a different approach to Shechem's sin. He felt that Dina was violated by one man, and the entire nation of Shechem should not have been punished. While it was just to punish the transgressor of a crime, punishing others who appeared to not have committed any sin at all not. After all, how will the other nations look upon the Jewish people when they see an entire nation punished for the actions of a few men? They will not only destroy Shimon and Levi, but now will hold the entire Jewish people accountable for their actions. This is why Yaakov states "I will be annihilated, I and my household. Now, since we held Shechem accountable for one man's actions, the nations of the world will hold all of us accountable for the actions of Shimon and Levi."
Now Yaakov's apparent cursing of Shimon and Levi in 49:6 of "with their congregation, do not join," can be understood. In Yaakov's opinion, Shimon and Levi, in their murdering the inhabitants of Shechem, had forgotten what the consequences of their actions might hurt the rest of Bnai Yisrael; that is, the congregation of Israel. Thus, the "curse" if Shimon and Levi was that the Jewish people should not join their congregation - that the rest of Bnai Yisrael not be affected adversely by the actions of Shimon and Levi.
As we journey through life let us all remember this outlook of Yaakov. Before one judges or punishes another, one must first ask oneself: does this person deserve this punishment? And, who will be affected by my actions?