Why is there death in the world? So that evil will not live forever.
Because, since we ate of the Tree of Knowledge, no one walks forward without stumbling, no one climbs without falling, no one does good all his life without causing some damage along the way. Until, at the end, our lives are an absurd muddle of good and evil inextricably bound.
With death, evil dies as well. The failures, the ugly acts and the damage done—all these wither and eventually perish. But the good we have accomplished—and that we truly are—this lives forever.—See Tzion B’mishpat, 5736