After a long and rather murky quest, a noted academic expert on religion thinks he's ""found it""; but readers may wonder. Needleman calls the element missing from Christianity (lost around the end of the Middle Ages, if not before) ""ontological love."" This he gropingly defines as ""the force within myself that can attend to both movements of human nature""--roughly, tuning in our inner and outer worlds--""within my own being, and can then guide the arising of this force within my neighbor in a manner suited to his understanding."" As a sympathetic Jewish student of Christianity, Needleman learned of this missing dimension through conversations with various Eastern Orthodox and Roman Catholic monks and priests, one of whom, the mysterious ""Father Sylvan,"" bequeathed to him a huge manuscript treatise on spirituality, from which Needleman quotes at disconcerting length. What Father Sylvan seems to be saying is that there are very few real Christians because in order to be a Christian you first have to be fully a human being, and there aren't very many of those either. The key to full humanity, in turn, is something a Zen Buddhist might describe as ""attention,"" the result of a demanding disciplinary process whereby distracting desires and childish illusions are set aside and all the energies of heart and mind are concentrated in a state of lucid receptivity to reality. One of the great advantages of this teaching is that it dovetails with so much of Eastern religion. The only catch involved is that, like most monastic counsels of perfection, it calls for a lifetime of unremitting practice and so (apparently) lies beyond the reach of the busy layman. In any event, Needleman's exposition, while full of personal warmth and candor, is unremittingly vague and diffuse. The esoteric depths of Christianity may well be lost, but at this rate they're going to stay that way.