However, what is the purpose of owning a firearm?
I think the purpose although somewhat irrelevant, is individually dependent. Why someone would carry a firearm is probably a better question, and in most cases (outside of the criminal element) I would say it is for some form of protection, either it be from the criminal, securing property or killing snakes.
What I think is very important, probably more so than skill level or proficiency, is knowing and understanding the laws regarding use of force, which are normally state specific, and vary greatly from state to state.