And much later, in a draft letter of 1963 (Letters no. 246), he [Tolkien] wrote:
'Frodo was sent or allowed to pass over Sea to heal him -- if that could be done, before he died. He would have eventually to 'pass away': no mortal could, or can, abide for ever on earth, or within Time. So he went both to a purgatory and to a reward, for a while: a period of reflection and peace and a gaining of a truer understanding of his position in littleness and in greatness, spent still in Time amid the natural beauty of '
Arda Unmarred', the Earth unspoiled by
evil.'