What is the meaning of having different narrations? What is each point that is different from the others?

The multiple narrations in
Frankenstein allow the story to be passed on, like the light of
knowledge, the dominant motif in the novel.

Here's how the
POV breaks down:

• Walton frames the novel by
  writing to his sister (and us, the readers) about
  Victor.


• In Walton's frame, Victor tells Walton (and us)
  about the Monster.


• In Victor's frame, the Monster tells
  Victor (and us) his feelings.


• In the end, Walton is left
  to carry the tale (the light of knowledge) back to the community of
  mankind


• If we didn't have Walton, the story would never
  reach us.  Who will deliver his letters to his sister?  (Victor and the Monster
  essentially die chasing each other on the
  ice)

The embedded narrative style is the only
way to get to the Monster and let the Monster speak for himself.  In this way, every
major character has a kind of first-person point-of-view.  In this way, the audience
gets all sides of the story to determine how knowledge should be
handled.

The multiple perspectives also determine the fate
of Walton, who is most like the reader and a foil for Victor.  All the while, we are
wondering if Walton will turn back in his quest for the pole.  Instead, Victor's
morality tale causes him to return to the community of man.  Does it do the same for us?
 (With the advent of human cloning, I wonder)...