A Myth is not a lie, but, like Art, a rendering of Truth. Subsequently, religion is the extension of myth through ritual. Despite the titles, these texts are as much about religion as myth, and the works are all the better for it. Campbell skillfully explores the Human experience, and what Man has made of it, over the course of these four seminal works. At times, one feels the influence of Toynbee, but Campbell has gone beyond the author of A Study of History and into a world all the more full of wonder.
Man is the most conscious participant in Nature, and, as the Image of God, the only creature capable of reshaping Nature according to his own interpretations of its meaning. These little shapings, which we call art, myth, religion, culture, and philosophy are the stuff a rich existence is made of.
Stated simply, this work dutifully charts the progress, derivations, and points of origin of these shapings. Campbell's prose is warm, friendly, compassionate, loving but stern, and creative. One could not ask for a better introduction to the Man's works.
Oriental Mythology is the second volume in the series, and probably the weakest. Campbell's familiarity with the subject is clear, but his ability to carefully balance his west-to-east/east-to-west thesis is a tad clumsy. The facts themselves are illuminating, as are his deductions, but the volume itself seems slightly awkward compared to the other three volumes. Don't start your reading of Campbell's work with this volume. (NOTE: You might also consider reading Volume Three: Occidental Myth BEFORE reading this volume. Such a reading might clue you into Campbell's style before delving into the depths of Oriental mythology.)
For those not familiar with some of the artistic themes discussed in this and other works, Campbell's Mythic Image (Illustrated Edition) makes a strong companion.