If we are going by Alex's purpose example ...
The purpose that you laid out seems very vague (too distant in the future). There are several ways to go about getting a respectable job, and providing for your family.
I mean if you want to get really specific ... The purpose of reading the book Principles of Accounting, is to get an accounting position where I can apply the skills that I learn in this book.
Of course you could always just say, I am reading the book Principles of Accounting so I can learn the methods of accounting, so that I can manage my personal budget and balance my checkbook. (practical application, and much better than Acing my next test).
