The military stuff is a McGuffin-type subplot. The real plot is the main character's obsession with seeing Lillian's vision of the afterlife.

The author of the screenplay, Bruce Joel Rubin, is a self-described spiritual teacher, and "transitional journeys" is kind of his thing. His three most well-known films (Brainstorm, Ghost, and Jacob's Ladder) are all about characters experiencing the afterlife in some way.