Gershon Loran had his first vision at 16 -- on the roof of his ramshackle Brooklyn apartment building. Orphaned at 8 by his parents' violent death in what was then Palestine, Gershon's only family were his aunt and uncle (his father's brother), and his beloved older cousin, who was to be killed in World War II.

Being pious Jews, his aunt and uncle naturally sent Gershon to parochial school. He was a docile, inwardly turned child, an unremarkable student who moved passively through each level of the orthodox school system, receiving ordination as well as a bachelor's degree in mathematics from an orthodox college. Then, because a friend suggested it, he went to a nonorthodox seminary, which bewildered his aunt and uncle. By now, Gershon was 21; it was June 1950, the beginning of the Korean War.

"The Book of Lights" is the story of Gershon's gradual intellectual and spiritual flowering, of the struggle of his soul between the rational everyday ethical world of the Talmud and the mystic religious imagination of the once forbidden Kabbalah, of his struggle to reconcile his inner voices to the world at large.

As always, Chaim Potok, author of "The Chosen," "My Name Is Asher Lev," "In the Beginning," and other fiction and nonfiction, is immensely readable. In this, his fifth novel, he weaves a compelling narrative of many disparate strands -- the dark whispering Brooklyn apartment; the intellectual ferment of the seminary; Korea; Hiroshima; Kyoto; a garden on a hilltop in Jerusalem; and always the imagery of red blazing fire and blinding light, as well as Gershon's visions and voices.

The shy seminary graduate goes to postwar Korea, where he is transformed into an army chaplain of formidable energy and ingenuity. He also becomes drawn into the tortured orbit of his old roommate Arthur, the son of a famous nuclear scientist. Arthur carries in his soul the guilt of Hiroshima. Potok balances man's ability to conceive of the blinding lights of Kabbalah's Celestial Chariots, against the blinding light that rained dead birds after Los Alamos and needlessly destroyed Nagasaki; the poetry and prophecy of the ancient visions against the witless cruelty of the rational mind -- and somehow makes one seem a preordained echo of the other.

This is a sad book without emotional catharsis. At the end, Gershon has finally made his choice. But it, too, seems preordained and ironically joyless. This tale is also puzzling in its uneven stitching together of fact and fiction -- Harry Truman, Albert Einstein, Arthur's father, the rescue of Kyoto, and in addition, the cursory treatment Potok accords several characters, especially Gershon's fiance, Karen. Furthermore, many readers may tire of the extensive quotations from the various Kabbalah tracts.

On the other hand, although Gershon's Korean adventure and his extraordinary vitality and genius for activating results do come as a surprise (to himself as well as the reader), Potok's own experiences as a U.S. Army chaplain in Korea serve him well in his description of life there, and of the cultural revelations that ensue when Gershon discovers a land completely untouched by Judaic tradition.

Potok is a persuasive storyteller. His people are etched with fine detail and he encloses them in a complete, separate, yet amazingly familiar world which we are able to visualize along with him. These are characters in whom we can immerse ourselves with great satisfaction. But the philosophical message is not always so clear and, at times, gets in the way of the narrative flow. Although one realizes fairly early the inevitability of the ending, it still is difficult to understand, in the larger philosophical sense, precisely what Potok is aiming for.