If you are quiet because your spirit is at peace and you are content with what is going on around you- It is good.
But if you are quiet because you are afraid to speak out, fearing that the words won't come out quite right, or that you don't understand exactly what is being talked about; that you might make an unintelligent blunder... that someone might laugh at something you say (that isn't really supposed to be funny) or even worse, respond sarcastically, please, please, please, listen to me.
Everyone (and really I do mean everyone!) that you are talking to has had moments when words don't come out right and when they are embarrassed about something that came out of their own mouths. I personally have about 10 comments a day that I wish I could retract. (Maybe there is something to be said for keeping your thoughts to yourself). :)
But you have so much to offer! The people around you don't realize the depth of your feelings, the passion that you have for life and love. The lyrics to the songs and poems you write often bring me to tears. I want others to know how absolutely amazing you are. I think that because you are so quiet, people don't know the real you.
And yet, they do. They'll come and tell me of your sweet spirit and your gentle smile, and your silent laughter when you think something is funny. They tell me you are brave when you share your soul through your writing. They say that your faith in God is inspiring.
And "they" are right. It is good. I love you, quiet one!