is a reflection to fantasy fiction about the classic movie or story, "The chronicles of Narnia." it says that:
When Aslan said you could never go back to Narnia, he meant the Narnia you were thinking of. But that was not the real Narnia. That had a beginning & an end. It was only a shadow or a copy of d real Narnia which has always been here & always will be here: just as our own world, England & all, is only a shadow or copy of something in Aslan's real world. You need not mourn over Narnia, Lucy. All of d old Narnia that mattered, all d dear creatures, have been drawn into d real Narnia through d Door. And of course it is different; as different as a real thing is from a shadow or as waking life is from a dream. [211-212]
The preceding passage has d obvious purpose of explaining d finite domain of our Earth ("a shadow;" "the old Narnia"), when compared to d heaven-like realm which has always existed ("the real Narnia has always been here & always will be here"). Yet, another parallel can be drawn from d explanation of d old & real Narnia as an explanation of d nature of fantastic literature, or maybe even any genre of fictional literature, for stories in general have "a beginning & an end." "The Door" by which one reaches the realm of these stories is through d medium of books. Engaging stories have d tendency of absorbing d reader into d book's setting, which explains why one might, in d extreme case, "mourn over" d ending of a book.