The Midrash Pirkai R. Eliezer, explains the significance of the four directions, what forces they each represent. The tribes were stationed were their attributes could either amplify the good or protect from the bad of the forces emanating from the four winds of the world. Back by the parshas which dealt with the initial construction of the Mishkan, it was explained how the Mishkan is a microcosm of the world. The protection provided by the tribes of Israel are that which protect the world. The east is where the suns rises.
Light is symbolic of Torah.
Understandably so, Moshe and Aaron's tents were in the east by the merit of their dissemination of Torah. The east is also the source of the harshest of the four winds. The greater the potential for good always means the greater the potential for evil. Even one Jew learning has what it takes to deflect those most devastating east winds. From the west comes the snow, hail, heat and frost.