"To be good is to do good."

This particular quote is attributed to Aristotle though he technically did not say it.  However, it does describe his philosophy.  The Greeks believed happiness was "living well and doing well."  While different from our modern definition is different it can still be related to our.  Part of happiness, according to Aristotle, was doing good things.  This led to self worth and meaning which then lead to a full life.  This contradicts Socrates who believed that simply being a good person allowed you to do good things.  Aristotle and Socrates both have good points.  Socrates states that the reasons people do unjust things is because they have a "disordered soul" which has many applications even now.  Aristotle states that we do good because it feels useful or happy which is a part of a "happy" life.
Aristotle also said that everything we did was to lead to our happiness and virtue was one of them.  I have to say that Aristotle was right in this regard.  Say that you want to be a doctor.  A person asks why.  That person responds to get money so that they can support themselves and be happy.  Maybe you will give a different answer such as helping other.  Again they ask why.  Eventually you answer that it will make you feel good and useful.  While both answers are different, they lead to what is truly desired a  fulfilling life.