The alchemist is represented here using Tarot imagery, in this case, the High Priestess, who taps the chest of the Thief, and causes something to resonate in him. The other figure, represents Mercury, the psychopomp.
Warning: NSFW for nudity (apologies if this is against the rules, staff.)
At the end of the movie, the alchemist gives the thief his tower, study, and laboratory. Presumably the thief is on the path to being an alchemist.
If we have not obtained immortality, at least we have obtained reality.