What happened to make Ephraim and M'nashe so special that the b'rachah uses their names? Certainly over the course of Sefer B'reisheet we can see the names of several great Tzadikim?
I heard this in the name of Rav Kook at a Shalom Zachor on Shabbat Vaychi.
Throughout Sefer B'reisheet a recurring theme appears amongst siblings - jealousy and envy
• Kayin and Hevel
• Yitzchok and Yishma'el
• Yaakov and Esav
• Yosef and his brothers
Finally, Yaakov favors the younger Ephraim and guess what? No jealousy, no envy, no vindictiveness!
Success at last. We have evolved to transcend sibling resentments. This is the reason "B'cha Y'voreich" due to this achievement at the close of Sefer B'reisheet.
Source text below:
כ ויברכם ביום ההוא, לאמור, בך יברך ישראל לאמר, ישמך אלהים כאפרים וכמנשה; וישם את-אפרים, לפני מנשה.