Most of that volume is committed to elaborating a theory of religion that, while refreshingly sound in its definition of religion, was already rather dated in much of its details when biologist Huxley composed it in the 1950s. In particular, he is greatly beholden to J.G. Frazer and that scholar's evolutionary systematization of magic-religion-science (e.g. 53-60, 96). He has a rather naïve view of historical religions as being each "the creation of a single personality" (82), and he does not impress with his facile dismissal of historical accounts of demonic possession as being uniformly attributable to "mental disorders" (94).
Still, there is much to like in this book. Huxley apologizes for an autobiographical chapter that demonstrates appropriate scholarly "reflexivity" far ahead of its academic time. And his ultimate solution to the conflict between traditional religion and modern science is to call for the formulation of a new scientific religion, of the sort invoked by Aleister Crowley's illuminist agenda. The comparison might seem strange, given Huxley's derision for the world-view of ancient and historical magic, but that world-view is not shared by Crowley's non-supernaturalist Magick, which instead emphasizes exactly the sort of criteria that Huxley advances for "Evolutionary Humanism." The Nietzschean "transvaluation of values" (201) for which Huxley calls is to understand that "Man's most sacred duty, and at the same time his most glorious fulfillment ... includes the fullest realization of his own inherent possibilities" (194).
The mention of "sacred" in the previous quote points up the fact that Huxley is indeed calling for a new religion, a sacred humanism, not merely granting a franchise of quasi-religious prerogative to secular humanism. There must be ritual, symbol, and narrative to appeal to the perennial human appetite for sanctity, and an intellectual apparatus to connect these with the ordering of society and personal discipline. Being trained in the methods of natural research rather than those of sacerdotal art, Huxley admits to not being able to formulate all of this from the principles that he hopes will ground it.
The point on which Huxley and Crowley are at odds in their visions of scientific religion is evident in Huxley's title. Crowley insists on the revelation that Huxley says we should do without. Huxley sees the institutional certification of "revelation" as grounding "the unfortunate tendency of ... religion to become an unduly conservative force, [which] has often led to religious thought and practice being below the general level of its times" (179). Crowley, by contrast, calls for revelation to become both epidemic and idiosyncratic: each man and woman should strive for his or her own life-governing message. And even when Crowley asserts the universal jurisdiction of the Thelemic revelation communicated to him (in Liber AL vel Legis), he cautions that each adherent should be at full intellectual liberty in the interpretation of that oracle. While Huxley rejects "the so-called revelation of Scripture" (88), Crowley's own new scripture instructs that "All words are sacred and all prophets true; save only that they understand a little."
In connection with Huxley's categorical dismissal of divine revelation, he also claims that "The beliefs of theistic religions thus tend inevitably to be authoritarian, and also to be rigid and resistant to change" (185). There have been in fact many non-theistic authoritarians (e.g. Stalinists) as well as theistic antinomians (e.g. Ranters and Muggletonians). As I've remarked elsewhere, authoritarian religionists will naturally insist that antinomians be disqualified as irreligious, but there's no reason to let the authoritarians own the category. If Huxley was willing to contest their ownership of religion, I don't see why he shouldn't have joined me and Crowley in doing so for revelation as well.