In his 2008 address to the graduating class at Wesleyan University, Barack Obama put it eloquently:

[O]ur individual salvation depends on collective salvation. Because thinking only about yourself, fulfilling your immediate wants and needs, betrays a poverty of ambition.

Watch his inspirational speech here:

[S]hould you take the path of service, should you choose to take up one of these causes as your own, know that you’ll experience the occasional frustrations and the occasional failures. Even your successes will be marked by imperfections and unintended consequences. I guarantee you, there will be times when friends or family urge you to pursue more sensible endeavors with more tangible rewards. And there will be times where you will be tempted to take their advice. But I hope you’ll remember, during those times of doubt and frustration, that there is nothing naïve about your impulse to change the world. Because all it takes is one act of service — one blow against injustice — to send forth what Robert Kennedy called that tiny ripple of hope. That’s what changes the world. That one act.