Sorry to dredge things up, but it appears I've been away for awhile.
What are you trying to do when you give? That is your purpose, not the act of giving. People can be charitable for selfish reasons. Charity isn't a purpose, it's an action. To what end are you being charitable? That is your purpose.
It's the same thing as saying skate-boarding is your purpose. That simply isn't be the case, your purpose could infact be self-glorification, self-improvement or a myriad of other things. Your purpose is the reason, not the action you use to achieve it.
Yep, because Charity isn't a purpose. Man can choose anything that is a purpose as his purpose. To preempt your next question, a purpose is anything that is an end in itself. Actions aren't purposes, they are means to achieving a purpose.
Words mean things. When you use them improperly, I will correct you. I'm just as fallible as you in this sense, but you can't expect people to understand you when you're unclear. I take alot of stock in using the correct word.