Thanks James, I always appreciate a skeptical reading. It's a puzzling scene. I only just realize that even if the mechanism involved was telepathy with the dead…or something…that still is not "Christian" as typically understood, and in the absurd effort to find LOTR is a Christian text, there is still a problem.

But I'd mention more info from Verlyn Flieger's paper. She notes that the scene appears to have no connection to the plot of LOTR and it's odd to have Merry become, for that one moment, the focus.

The episode, she says, was composed around the time as explicitly reincarnational themes in other Tolkien stories, which she thinks it resembles.

She says an earlier draft of LOTR has Merry say at the same scene: ‘I begin to remember... I thought I was dead—but don’t let us speak of it.’”

As Merry has relived the memory of some warrior dying in battle, she attempts to locate this battle in Tolkien's pre-history of the spot. An appendix appears to provide the answer: “A remnant of the faithful among the Dúnedain of Cardolan also held out in Tyrn Gorthad (the Barrow-downs)” (RK, Appendix A, I, iii, 321).

This does not seem to provide any link to an ancestor of Merry. So it's not an ancestral memory. It leaves a total mystery as to why Merry was having this experience, or why he has identified with it so strongly—as if it was his own body being attacked.

So she comes to the view that reincarnation is the most likely interpretation.