Edwards IIRC had some interesting theories about Satan. That this now-fallen angel was originally intended to be the savior of mankind, but since he dropped out of heaven, Jesus had to do the job.
Sorry to keep beating this horse (I really do admire Edwards, and am wanting to know if he's got some heresy in his writings)....
So it looks like Edwards found a Scriptural reference to Lucifer as having been "annointed," which contains the same root-word as "Messiah." Therefore, the pre-fallen angel of light Lucifer was a type of "Messiah" (by the very etymology of the word) -- which is entirely *entirely* different from "Savior."
Make sense?
Thanks for bringing that up -- it's good to delve into rich theology like this!