My roommates and I spoke for two hours last night about the Holy Ghost and ended on one last question we could not answer. So I offer it to anyone who maybe has heard the insight we are missing:
What is the true purpose of the Holy Ghost within the Godhead? Why can’t Heavenly Father and Jesus Christ fill all the needs the Holy Ghost has?
The Inconvenient Study 
Adam
/ December 1, 2010I posted a link to this one on Facebook and got a few responses and emails. So I’ll post them here for anybody else who may only see the blog side of things and would like to comment.
Dan –
Just off the top of my head, a good place to start would be with the advantages the Holy Ghost has as an unembodied being. This could relate to God’s omnipresence, for example, which is only possible through the ministry of the unembodied Holy Ghost. Also, perhaps because of this he is able to influence us (i.e. fruits of the spirit, confirming truth, etc) in a way that the embodied Father and Son cannot.
Adam –
Well our question came because in Gospel Principles it says that the personage of the Holy Ghost can only be at one place at a time, which I think then means the Holy Ghost has an outward influence in itself, but if that is so then why can’t the Father and Christ perform that influence themselves instead of relying on the Holy Ghost?
Adam –
I’m sorry, Gospel Principles actually says that it’s influence can be felt around the world. I don’t mean to take credit for that.
Kegan –
Yeah, I would have to say that the most basic answer I can think of is that the Holy Ghost doesn’t have a physical body. Both Heavenly Father and Jesus needed to get bodies in order to fulfill their missions and be who they are. For reasons other than that, I’ll have to do a little research.
Jeremy –
[ . . . ] At least as I understand it you’re right (and I would assume we understand the Gospel Principles manual), the Holy Ghost is only in one place at a time. And as I understand it, the method by which the Holy Ghost ministers to so many people at once is something the Father can do as well.
As for reasons the Holy Ghost needs to be without a body, the only reason I know of, is at least in the instance of temporary transfiguration, we need a disembodied perfected spirit to share our tabernacle with us, something the spirit of a resurrected being cannot do. It was a necessary part of the plan that at least a few mortals testify of the reality of the Father and the Son, and the Holy Ghost would help quicken them in order to abide the glory of the Father and the Son. (D&C 67:11)