It is a novel of great depth, a work without bottom, written in a mythic omniscience bristling with Old Testament rhetoric and deadpan metaphor.
It is first an historical western novel, the characters and events built upon the scalp-hunting expedition in Samuel Chamberlain's autobiographical narrative, My Confession. Scholars, led by John Sepich's own great work, Notes On Blood Meridian, have shown that McCarthy used a wealth of other historical sources as well and the structure of Blood Meridian, as well as the secondary title, are in part parody of the style of early western narratives.
Scholarly book-length studies have also been published arguing a great variance of philosophical interpretations: Christian, Buddhist, Nihilistic, Marxist, and Gnostic among them. All of these are equally valid, for the novel has Faulkner-like recalcitrance at its core and it defies definitive claims and explanations. Like all great literature.
The autobiographical and historical Suttree was McCarthy's first novel, though not the first published. His first three published novels, The Garden Keeper, Outer Dark, and Child of God, represent a trilogy of lower man, flesh-and-blood man. In metaphor, they concern the evolutionary Fall of consciousness into animal man.
Like Dante and James Joyce before him, the grand mosaic of McCarthy's work is animal man, middle/heroic man, and spiritual man. He is not concerned with the evolution of intelligence; he is concerned with the evolution of consciousness, from id-dominated man, to ego-dominated man, to superego-dominated man. Blood Meridian is the dividing line between the animal man trilogy and the middle/heroic man trilogy. His later works, from Cities of the Plain on, would involve a more spiritual, a more reflective consciousness.
McCarthy's writing style evolved at the same time, from the Faulknerian of his early gothic works to the Hemingwayesque of his heroic Border trilogy to the Beckett-like spareness of his later works. The dividing lines are not clean cut--nor were they in Joyce--but the mosaic is there, the increasing empathy, the evolution of consciousness.
As with some of Faulkner's novels, McCarthy's works can often be broken into their common denominators of time and space while linked to the author's own history. See Dr. Jay Ellis's brilliant book, No Place For Home: Spatial Constraint and Character Flight in the Novels of Cormac McCarthy. The spaces collapse until the characters run out of country. Also see Animals in the Fiction of Cormac McCarthy by Willis R. Sanborn, which shows how animals increasingly die and disappear in each McCarthy novel published.
As with all great works of literature, you can take one page and write pages about it. Blood Meridian's opening line is, "See the child."
Like John Sepich, I believe that Blood Meridian turns on the episode where the kid shows mercy to the eldress in the rocks. Despite being then twenty-eight years old, the narrator refers to him as the kid until then. Thereafter, he is called "the man."
According to Elizabeth Francisca Andersen's book-length study, A String in the Maze: The Mythos of Cormac McCarthy, this phrase is ecce puer which becomes ecce homo. Elsewhere in the text, McCarthy repeats the 'See him' as a form of Ecce homo, behold the man, from John 19:5:
"..the phrase used by Pontius Pilate in presenting Jesus to the crowd demanding his execution. The phrase Ecce puer (Behold the child.) appears in the Old Testament (Isaiah 41:1) in a passage that has traditionally been read as a prefiguration of the miracles performed by Jesus. Ecce Homo has been used since the Middle Ages as the title for paintings depicting suffering, poverty, illness, and death. Among the many works that take Ecce Puer as their title is a poem by James Joyce. Ecce Homo is the title of a book by Friedrich Nietzsche, who employs the phrase ironically. Both works may have been known to McCarthy."
McCarthy's next novel was All the Pretty Horses. It is a very deep novel and it represented the next stage in the author's mosaic, the first novel in a heroic trilogy. A segment of McCarthy fans, hooked on the style of Blood Meridian, were stunned and turned off by this development. They objected to the shift in the prose style. They cried "sell out!" and stomped off from the Cormac McCarthy Society in a huff.
Much later again, when McCarthy published No Country For Old Men, there were similar cries and people who swore at him for being a sell-out to commercialism. But that novel, genre on its surface, is also miles deep, and it fills its niche in McCarthy's greater mosaic of the evolution of consciousness. Chigurh is the id-dominated man, Moss is the ego-dominated man, and Bell is the superego-dominated man. But it is Bell's book. A close reading of the opening page shows that Bell has empathy for both the victim and killer, even though the killer himself is a psychopath.
The mosaic of Cormac McCarthy's fiction is the evolution of consciousness and the cyclic spectrum of the human condition from animal man to middle/heroic man to spiritual man.