You guys are missing something key here. Brion's work seems big on symbolic imagery. It's not really religious (I think Brion was on record once saying he doesn't believe in gods, meaning anything from a Buddhist or Taoist mindset, to nontraditional belief, to agnostic, to atheist) so much as a sort of powerful imagery.
There are things in our lives that are immortal. What is the first thing coming to mind? Depression. No matter how many times, it always comes back. People with other difficult to solve disorders like mania or hallucinations probably feel the same.
This is not to say that Crest can solve their problems by therapy. It's saying the same approach works. How do you deal with something immortal? Well for the long term you figure out its source of power. Only something that truly is a deity is self-powered, everything else that is immortal has some Achilles Heel (like they have to feed regularly, or they need people there to remember them, or they're allergic to milk (who knows what movie I'm talking about)). Maybe a final boss type deal, getting rid of the evil thing in our life that won't go away. But for the short term, the solution to such a creature is one of three things: get past it, trap it (sealing is a big option in games like Final Fantasy V), and strip it of its power (the last of these sometimes overlaps with a permanent solution, unless it is able to regain power).
Update: Everyone watch the anime Lost Song. It gives very good insight on what it's like to be immortal.