The Midrash offers a parable in explaining the use of olive oil for the Menorah in the Temple: it is comparable to a king whose legions rebelled against him. However, one of his legions remained faithful and did not rebel. The king said, "From this legion that did not rebel, I will take for my rulers and governors." So did G-d say, "This olive brought light to the world in the time of Noah, as we see ‘the dove came…and it had an olive branch in its mouth’ (Vayikra Rabba 31:10)."
One commentary (Rabbi Dovid Luria known as the Radal) explains that the corruption preceding the great flood did not affect man alone, but also the animal and plant kingdoms. Different animal species tried to interbreed; plants attempted to intergraft. Only the olive branch resisted all forms of grafting. Thus, it is considered the “legion that did not rebel.” It remained pure. Because it remained faithful to G-d, the olive was chosen to be the sign of rebirth and renewal after the flood. It was chosen to be the source of light in the holiest place in the world, and the source of light for generations to come.