In the beginning of Parshas VaEirah the Torah tells us the children of Reuven, Shimon, and Levi. With Levi the Torah goes into great detail and then does not continue with the other Shevatim. If the whole purpose was to document Moshe and Aharon's lineage why start with Reuven?
Rav Eliezer HaGadol Ashkenazi in his classic, Maasei Hashem, says that the Torah is teaching us why Levi's descendants played a central role in Yetzias Mitzrayim and not the descendants of his older brothers. He says that Levi foresaw and felt the pain of the upcoming Tzaros and gave his children names hinting towards the galus. Gershon, that they would be strangers in a strange land; Kehos, weak and battered; Mirori, they would lead bitter lives.
This is seen in the wording of the parsha when documenting each family. By Reuven it says, "The heads of the families were..." By Shimon it says, "The children of Shimon..." By Levi it says, "These are the names of the children of Levi." It was the tears shed behind these names that not only helped save his family from being pulled into slavery, but it also made this family the worthy redeemers of the Bnei Yisrael.
It says in the last perek of Yeshaya (66:10) regarding the Binyan Bais HaMikdash, "Sisu Ita Masos Kol Hamisablim Aleha; Rejoice those who mourned over her." Those who cry most in the Galus are the ones who are zocheh to merit rejoicing in the Geula.
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