Have Mental Health Questions? Ask a Psychiatrist Online
Hi there! I hope to be of some assistance to you... the answer to your question could be answered in many many ways, depending on who you ask... the Dalai Lama would say it is to help others, and to be happy... wondering why you ask?
Here is a video by a rabbi who talks about this very question: http://www.oprah.com/relationships/Why-Life-Is-Worth-Living
I wish you all the very best :-)