She knew from a young age that her sole 'purpose' (in life) was to be a writer. [=she knew that all she wanted (in life) was to be a writer]
We were happy to know that the money was being used 'for a good purpose'. [=for something useful, important, etc.]
There's little/no 'purpose' in restarting the process. [=there is little/no reason to start the process again]
(..) The house and grounds are left to the city of Gotham on condition that they never be demolished, altered or otherwise interfered with... and that they shall be used for one purpose, and one purpose only: the housing and care of the city's at-risk and orphaned children. My clerk can help anyone with (..)2012 The Dark Knight Rises