Every life must struggle with the conflict between how large our private ego existence seems to us and how insignificant it is to the universe. To ourselves our conscious existence is indescribably important, it's everything, but the universe doesn't notice as it shuffles us off into untimely oblivion.
A common way people cope with this dissonance is to stretch their identities beyond the ego boundary and combine it with larger and more permanent things. A natural example is a parent that places the well-being of their family above their own well-being. Others may identify with their nation or religion. People of a more idealistic personality type associate with an abstract principle like "justice" or "the good of mankind" (quite a few of my friends choose "science").
Identity-stretching is an effective way to cope with an uncaring universe. When the hazards of the world inevitably come upon us and threaten to snuff us out, we take comfort that some part of our larger identity lives on regardless of what happens to our body and consciousness.
But identity-stretching is not just a coping mechanism. It ennobles us. Nobody is remembered for the things they did only for themselves - for the meals they ate, for the media they consumed, or for the other comforts they enjoyed. Rather, they are remembered for the works they did in service of art, love, truth, or justice. Great deeds only proceed from great souls.
Extending your concerns outside your self boundary is the first step in becoming beautiful, heroic, or holy. It puts us in communion with the universe, the gifts of the past and the hope of the future. We become a phrase in the greatest narrative, instead of the totality of a trivial one.
This ego-growth is a boundary between childhood and adulthood. The child holds nothing above his own momentary well-being. But any animal can care about the fullness of its stomach. A person matures when he develops purposes beyond that, a character trait that is distinctly human.