Heavenly host in the arrivals lounge

They come like heralds of the millennium; a plague of angels. Angels on books (indeed on this very book), CDs, stamps, postcards, packets of crisps. Where do all these monsters come from? Our angels do not guide world leaders or advise foreign policy, they do not serve as divine messengers. They are happy to hang around as scraps of ephemera, awaiting the end. But Harold Bloom, in this remarkable book, argues that the craze for angels is more than a transcendence motif of American capitalism. It is an extraordinary flowering of latent Gnosticism that could hurl us well into the next century.

Bloom diagnoses the popular obsessions with angels and aliens, prophetic dreams and astral projection, "near-death experience" and other-worldly abduction, with knowledge drawn from the fractured traditions of mysticism. He offers the wisdom of millennia to probe this excitable talk, rather than allowing the supernatural, the imaginative, and the creative to be hijacked by incoherent, New Age cranks.

The next millennium is made in the image of such concerns. 69 per cent of Americans believe in angels and 46 per cent claim to have their own guardian angel. For Bloom, these figures are not monstrous specimens for clever-clever cultural analysis; he simply notes that "all of them have distinguished forerunners in venerable traditions". He seeks to recover these traditions. The purpose of Bloom's book is to "raise up and illuminate these appearances in order to save them, by returning them to the interpretative wisdom of the Christian Gnostics, Muslim Sufis, and Jewish Kabbalists".

The cosmology of the pre-industrial West becomes alive. "How is it that Ezekiel and Daniel, and the Gnostic, Sufi, and Kabbalist sages and Saint Francis and Saint Teresa and Joseph Smith, could see angels, and we cannot?" Bloom does not doubt that Zoroaster and Smith saw and heard angels (though he is more sceptical of many current encounters - angels now seem too promiscuous), but why have miracles and angels fled (or been exiled from) our intellectual and artistic life?

So Bloom is offering to explain gnosis to those who may have experienced it, yet do not know what they know - who, it turns out, might be most of America. The country is in a fit of Gnostic rage and misery, typified by the anxiety of Generation X: "the burdens of a society that is weary with its sense of belatedness, or 'aftering', a malaise that hints to us that we somehow have arrived after the event."

Gnosticism is derived from the Greek gnosis - knowledge (hence its more familiar opposite, "agnostic" - knowing nothing about ultimate reality). The aim is to know God through knowing oneself. The Gnostic begins in melancholia - a sense of having been thrown into this existence - but this heaviness is lightened by the recognition of an ancient and divine spark in the self: the activity of self-knowledge reveals one's divinity, and at the same time one's capacity for self-knowledge confirms it. Dreams, revelation, ecstasy, inspiration - all guarantee one's primordial godliness. The book is peppered with angels of the most colourful and polemical theology. Bloom charts the influence of Zoroastrianism (c.1500 bc) on Judaism, Christianity, and Islam, and suggests that as angels originated in the Iranian millennial religion, so they now return. The Zoroastrian angels, canonised by the Jews, were watchers or messengers, terrible and divine, powerful and wilful creatures who lusted after women.

The Catholic angelic order was clarified by the fifth/sixth-century Neoplatonist Pseudo-Dionysius, who forged texts supposedly written by Dionysius the Areopagite, converted by Paul (the forgery was not discovered until 1457). Meanwhile the tradition of the fallen angels derives from an essay by Apuleius on Socrates's other-worldly inspiration, his "daemon". Satan developed from a righteous prosecutor, in no way evil, but was gradually puffed up into a rebel by commentators like St Augustine. The court attorney or diabolos (Greek for "blocking agent"), was transformed into a principle of evil, the subtle serpent at the root of the creation.

Bloom's genealogy of Enoch, who ascended as the god-angel Metatron, is the strongest part of the book - a wonderful expedition into the crooked corners of angelology. But exhausted by this conjuration, Bloom turns to sleep: to dreams and near-death experiences. Until Freud, dreams were routinely interpreted as prophetic. Freud endeavoured to make dreams profoundly nostalgic, and in doing so ironically established his own status as a prophet of the new psychoanalytic science. For Freud there was nothing to foretell - all was in the past - it is a betrayal avenged in the prophetic dreamwork of angels today. Bloom's analysis of the "near-death experience" (including a droll account of his own trip to the shining light and back again) also seeks to recover the Gnostic constitution of the astral body from contemporary faddism and anecdote, which stymies the possibility of ancient knowledge.

Omens of Millennium is a deeply personal testament. And though filled with almost proverbial insight, gentle wisdom, and melancholy wit, it is a powerful refutation of a God who could permit the Holocaust. Without Bloom's light erudition, this would be crankery of the most fatuous kind, but he seeks to excuse God the catastrophes of the world and return us to the other, human, god-angel, Metatron. Bloom concludes with a Gnostic sermon: "Not by Faith, Nor by the Angels". End the reign of angels; they are not our guardians, but our jailors.

Bloom invites us to recover the most ancient mystery of being, buried deep inside us. Perhaps, as said in the Gospel according to Thomas, "He who shall find the meaning of these words shall not taste of death".

Nick Groom is lecturer in English and American studies, University of Exeter.