Originally Posted by stoffe
Charisma is a measure of willpower and force of personality in d20. So presumably you'll have a better ability to shape and command the Force if you are strong willed.
Re: Force of personality
I've always understood charisma to be applied in interpersonal situations in order to improve a character's ability to coerce, convice, entice, seduce, intimidate, etc. someone else. After all, what is a personality if there no other person around?
Re: measure of willpower
Meanwhile willpower is a mental or spiritual fortitude and is completely intrapersonal. Note that your Will saves only get bonuses from you Wisdom modifier, not your Charisma modifier.
If Charisma is an interpersonal statistic, it should have no place in influencing an impersonal Force. Wisdom should be the only statistic used.