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]
(..) - Were you not sent for? Is it a free visitation? Come, deal justly with me. Come, come. Nay, speak - What should we say, my lord? - Why, anything but to the purpose You were sent for, and there is a kind of confession in your looks... ...which your modesties have not craft enough to cover (..)2015 Hamlet
(..) And for this time of meeting, thus much the business is We have here writ to Norway, uncle of young Fortinbras, who, weakening and bedrid... ...scarcely hears of this his nephew's purpose, to supress his further gait herein And we here dispatch you, good Cornelius, and you Voltemand... (..)2015 Hamlet