The context of Emerson's quote helps to reveal its significance and overall meaning.  Consider the full nature of the idea:

There is a time in every man's education when he arrives at the conviction that envy is ignorance; that imitation is suicide; that he must take himself for better, for worse, as his portion; that though the wide universe is full of good, no kernel of nourishing corn can come to him but through his toil bestowed on that plot of ground which is given to him to till. The power which resides in him is new in nature, and none but he knows what that is which he can do, nor does he know until he has tried.

For Emerson, the idea of envying another is borne out of ignorance.  If individuals recognize the "wide" and divergent nature of the universe, they can embrace that which is good and foster their own path out of a world in which so many seek to imitate others.  The notion of imitation being suicide resides in the idea that when individuals commit to the need to "make themselves for better," there is a sense of independence of action and decision that is intrinsic to individual identity.  When individuals imitate others, they end up embracing something that is not their own.  When individuals commit to the idea of following another, they lessen what Emerson sees as a vital part of identity.  For Emerson, envy that is borne out of a desire to have what another has or imitating another removes the fundamental power of the human being.  It is here where the quote asserts that individual freedom and individual identity are essential components to one's character.  The theme of individualism is powerfully demonstrated in the quote.  The better the chance that one recognizes this fundamental "power" and strays from imitation and envy, the better the chance one can find happiness in this life in Emerson's understanding.