From publisher blurb:
Many Faiths, Many Truths
In the world of Eberron, the reality of the gods depends on the belief of the followers. Contradictory truths might both be correct. Vague legend might be fact, and accepted fact only dogma. But to every worshiper, the divine presence manifests in miraculous magic, boons for the unfaithful, and undeniable holy power.
In short, faith shapes reality.
This supplement presents detailed descriptions of the major religions of Eberron, including the rival pantheons of the Sovereign Host and the Dark Six, the young faith of the Silver Flame, and the shadowed Blood of Vol. You'll also find intriguing details of lesser religions, such as the beliefs of the laconic warforged, the mad cults of the Dragon Below, and the various druid sects of the Eldeen Reaches. Faiths of Eberron also includes new feats, spells, prestige classes, and equipment to give more options to devout worshipers and sometimes followers alike.