Suddenly my whole body began to shudder, not the skin with its surface movements but the deep flesh and bone, a repeated convulsion that turned me sideways, then around. My knees struck solid earth and I felt cloth and flesh tear. .. It was the god. He had come. What was this? A yell, my chest pumping out air, the muscles convulsed again.... I spoke to the god who had laughed: 'Have mercy!' and it was so strange to feel that same mouth which had opened and bled at the passage of the god's voice could now make words for a poor woman on her knees. (p87-88)
Ionides plans to use the oracle network to persuade mainland Greece to free itself from Roman rule. Arieka may be the gods' tool but she refuses to be the priest's --- is at first bewildered by, and later quietly dismissive of, his disbelief. The Propraetor Lucius Galba (an atheist, by his conduct) insists that priests and oracles confine themselves to 'religious duties' -- and, unlike Ionides, he does not perceive those duties to include wider concerns of patriotism, nor the reinstatement of theocracy.
But that's only one level of the plot. The novel also deals with Arieka's relationship with the god, or gods, she serves: her ignorance of what she speaks in trance, her dismay at the gods turning away from her (from Greece), the way that she and Ionides become like an old married couple without ever being anything but Priest and Oracle to Apollo.
The supernatural, the divine, is never explained, for Arieka accepts it for what it is: as real and vivid as any other aspect of her life. There's more mystery, for her, in finding a chest of tablets inscribed with Hittite characters -- left untouched since the early days of the Oracle -- than in swaying upon her tripod and speaking in a voice that isn't her own.
There's a section missing halfway through the book, and I can't help feeling that Golding would have polished and tightened and smoothed the text, possibly at considerably more length: the final chapters seem less 'finished' than the rest of the novel. Fascinating, though.