What does this quote mean? "The most powerful thing that can be done is to name something."
It means "If you name something,you do the most powerful thing(can be added "in the world")" I think, the name verb in this quote is about giving a name to something.
When I read the quote, I immediately thought of A Wizard of Earthsea by Ursula K. Le Guin, a fantasy novel in which the most powerful magic (real magic, that can actually alter reality, as opposed to illusion) is made possible by knowing something's true name. In mythology, some demons are also "bound" by uttering their true names.
However, while the components of the sentence can be analyzed, it's not possible to say what the quote actually means without knowing its source. (It's likely a metaphor for something; knowing the source would tell us.)