Dear Sara,
At first take my love. I hope you are well. I received your letter just now. You wanted to know about my aim in life.
The aim of my life is to become a doctor & serve the poor villagers. Most of the people of our village are poor & illiterate. So they don't get help & advice of a good doctor. They suffer from many diseases. I want to help them by treatment. So I decided to be a doctor in future.