I would suggest a question: what is your life for?
As to mathematics, well... history of the universe can be described by one single word: assembling. Be it assembling of particles into atoms, or atoms into compounds, or peoples into societies. Eternal process of assembling. And parts of mathematics are needed for development of human civilization i.e. for continued assembling. And other parts are... well... we all produce garbage, be it in life or in mathematics.
Don't ask what is assembling for. This is like an axiom. All the rest are like theorems, i.e. the question 'what is it for?' is applicable.