When the Jewish People are united there is no power in the world that can oppose us. But when there is dissension, we fall in front of our enemies like wheat before the plow. G-d is One. His name is One. But when hate divides us, not only do we cease to function as a nation, to reflect G-d's Unity, but we cease to serve any function at all.
History is like an enormous pond.
Every action makes an impact on the world like a pebble thrown into the pond. Just as the size of the ripple depends on the size of the pebble and the power of the person who throws it, so too an action's impact on reality depends on the stature of the person and the nature of his action. The fathers of the Jewish People were spiritual giants whose actions created ripples that we feel to this day. Yosef's encounter with his brothers created a ripple which would be felt by the Jewish People across the millennia. In this week's Parsha it's difficult to understand why Yosef is so hard on his brothers.