Knever

Question: I have played through the game several times and viewed this movie at least five or six times completelty, but there is something major I still don't understand. What is the fountain of "water" that appears in the Church and cures the geostigma near the end? The pool that appears right after Kadaj blows a hole in the ground. Is it lifestream energy from the planet? It is the presense of Aerith? What is it? It plays such a huge role but isn't explained at all.