Therefore our original storehouse consciousness was pure, but it has become polluted with the accumulated consciousnesses of each of our lifetimes (= karma), which causes rebirth.
So we need to relinquish what is in our storehouse consciousness from all of our previous lives (clear all past karma) in order to be like an arhat (not generating new consciousness), and thereby reach nirvana.
When we are no longer attached to the notion that we have a self, as our consciousnesses are dependent on each other, then we have attained wisdom.