Minor Works -- 2 - Leaf by Niggle

[Guinevere]

This sentence from Tolkien's letters ties in nicely with Niggle's Parish:

from letter #45 to his son Michael, written in June 1941:
"There is a place called "heaven" where the good here unfinished is completed; and where the stories unwritten, and the hopes unfulfilled, are continued."

So he had this idea, years before writing "Leaf by Niggle"!