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]
(..) You do. You see people. l see you. And ? You wouldn't have jumped. But the purpose of university is to find a suitable husband. Rose has already done that. Here comes that vulgar Brown woman. Quickly, get up before she sits with us. Hello, girls. (..)1997 Titanic