What is the purpose of life?

I was waiting at a Govt. Office. That day I was quite down, flood of memories, melancholy. During such moments, I start feeling disinterested in everything. My mind stops seeing a purpose for anything. So I sent an SMS to  friend of mine, who is a Doctor. This is the conversation we had:

Me: Doc, what is the purpose of life?

Doc: To eventually die <she thought I was trolling with that question>

Me: So why do we have to get attached with things to only get detached, why do we have to struggle, go through happiness and sadness, why do we have to win and lose, why do we feel like pleasing others and expect others to please us, why do we have to do all that we do?

Doc: Coz if not, we would be God!

Me: You mean God sits and does nothing and we are here to go through this cycle of momentary sadness and happiness ?

Doc: Yes, to sit quiet and not do anything, you got to be up there!

Me: But if sadness and happiness are momentary, what is there to look forward to in life? Where is the motivation when the end result is death?

Doc: When you are sad, look forward to the happiness and when you are happy, enjoy while it lasts, coz sorrow is lurking somewhere around

Me: We always want happiness, not sorrow. Happiness is like rare things: gold, diamond, platinum..All the struggle and sorrow we go through is to experience momentary happiness. This makes life materialistic,to seek happiness.Sucks.

I guess Doc got busy after that and there was no reply. I continued with my work, going through a cycle of happiness & sorrow. Living.