I agree, it is an interesting quote. It fits with what I read in the scriptures: "spirit" doesn't always mean literally a spirit body (with fingers and toes, etc.). Sometimes it means something sort of like "feeling" or "attitude," but deeper. For instance, the "spirit of contention" is not a person, even though it certainly is Satan's spirit because it's the kind of spirit Satan has. I think that's what Joseph F. Smith means by "light of truth." Light illuminates, and the light of truth is that which enables you to see that which is true, which is part of what the Holy Ghost communicates to us. Sometimes I interact with people of other religions who are very, very good people who see truth clearly and act with great courage and integrity. I think the "power and light of truth of the Holy Ghost" is precisely the spirit which rests upon such people when they are acting this way. The gift of the Holy Ghost is the legal right to have just such a spirit at all times, provided you don't purposefully reject it. (Rejecting it is simpler and more common than one might think. When your alarm is beeping at you and you KNOW you should get up, hitting "snooze" is rejecting the correct course of action, and is in my opinion a case of someone desiring not to have the correct spirit. I am not guiltless in this matter.)
"The presentation or 'gift' of the Holy Ghost simply confers upon a
man the right to receive at any time, when he is worthy of it and
desires it, the power and light of truth of the Holy Ghost, although
he may often be left to his own spirit and judgment." --Joseph F.
Smith (manual, p. 69)
Be pretty if you are,
Be witty if you can,
But be cheerful if it kills you.