How far that little candle throws his beams!
So shines a good deed in a naughty world. — The Merchant of Venice, Act V, Scene I

My Take – To a lot of people, a good act, even just a kind word to be polite, can mean a lot.  We are bombarded, both by the media and in our lives, by darkness and conflict.  By being good to someone, you bring a little light into their lives.