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]
(..) He has chosen exile. You are no Elf. Men of the South are welcome here. -Who are you? -I am a friend to Gandalf the Grey. Then we are here on common purpose... ...friend. The shards of Narsil. The blade that cut the Ring from Sauron's hand. It's still sharp. But no more than a broken heirloom. (..)2001 The Lord of the Rings: The Fellowship of the Ring