BOOK REVIEW - Probing America’s Religions - THE AMERICAN RELIGION: The Emergence of the Post-Christian Nation, <i> by Harold Bloom</i> , Simon & Schuster, $22; 288 pages

Religion is not a matter of what we do out of habit or duty--it is, by definition, what we hold to be true in our hearts and souls.

Nowadays, of course, we may place more faith in the powers of law and psychiatry than in prayer and communion. So the most pertinent question to ask about religion in America today is: What do we really believe?

Harold Bloom tries to tackle this question in “The American Religion,” an intentionally provocative study of the innermost meanings of religion over two centuries of American culture.

Bloom is an English professor and a literary critic by profession. Last year, in his admirable “Book of J,” he applied his high-test critical skills to the hidden texts of the Bible and came up with a surprising, provocative and important rereading of Scripture in which he likened the original flesh-and-blood author of Genesis to Shakespeare and Kafka.

Now Bloom styles himself as a “religious critic,” whatever that is supposed to mean, and offers up “The American Religion” as his pronouncement on “the irreducibly spiritual dimension” of religion in American life. Our “obsession” with religion, Bloom insists, holds out the prospect that “the 21st Century will mark a full-scale return to the wars of religion.”

The central conceit of Bloom’s new book is that American civilization has spawned its own peculiar theology--a self-centered and inward-directed spirituality which Bloom characterizes as a fusion of Gnosticism, an early form of revivalism called Enthusiasm and something Bloom dubs “American Orphism.” And, despite all the stay-together-and-pray-together sermonizing by American clergy, Bloom insists that what really matters in the American religion is a strictly private and personal spiritual experience that he sees as dangerously anti-democratic.

“We are a religiously mad culture, furiously searching for the spirit, but each of us is subject and object of the quest, which must be for the original self, a spark of breath in us that we are convinced goes back to before the Creation,” he writes.

“Urging the need for community upon American religionists is a vain enterprise; the experiential encounter with Jesus or God is too overwhelming for memories of community to abide, and the believer returns from the abyss of ecstasy with the self enhanced and otherness devalued.”

Bloom is a relentless phrase-maker, and he stokes up the prose in his new book with knowing historical and literary allusions and frequent rhetorical flourishes. Thus, for example, we are treated to Bloom’s passing reflections on “the troubling near identity between the religion of violence and the violence of religion”--and sometimes the reflections pass a bit too quickly to make much sense.

Still, “The American Religion” is enriched and enlivened by the curiosities of American religious history, a subject that clearly fascinates and horrifies the author.

Bloom uses his essay on the inner meaning of American religion in theory and practice as an occasion to recall some of the odder manifestations of faith in the New World.

Bloom ponders the Perfectionists, the Shakers, the Pentecostals, the Black Muslims, the miscellaneous cults of the New Age. He peers into the mysteries of Christian Science, Seventh-day Adventism, the Jehovah’s Witnesses.

And he undertakes an extended deconstruction of the Mormon and the Baptist churches, neither of which will be delighted by his sometimes caustic appreciation of their role as “the two crucial branches of the American religion.”

“To me, culturally an American Jewish intellectual but not an adherent of normative Judaism, nothing about our country seems so marvelously strange, so terrible and so wonderful,” he writes with characteristic irony and a chilly critical aloofness, “as its weird identification with ancient Israelite religion and with the primitive Christian Church that came out of it.”

Harold Bloom, a controversialist by nature, is the author of about 20 books on subjects ranging from the Kabbalah to Blake to Wallace Stevens, but last year’s “Book of J” is an especially hard act to follow. As a fresh reading of the holy writ of three religions, “Book of J” was a work for the ages.

By comparison, “The American Religion”--a fretful essay on the dark side of spirituality in a democratic society--is more nearly an op-ed piece.