Although this section is told from Ralph's point of view, the speaker in the quote is the novel's narrator. Immediately before this paragraph, Ralph, with Jack and Roger, is heading up the mountain and has almost arrived at the site of what they think of as the beast. At this point, we are inside Ralph's head as he hears a chattering sound, then screws up his courage and takes two "leaden" steps.
As the quote begins, the narrator takes over. It is as if Golding is switching to a different camera and drawing back to show the wider scene. We know this can't be Ralph's point of view, because the narrator says that the moon is behind him, rising on the horizon. This is not something he or the other boys see, but the narrator wants us as readers to know the lay of the land. The narrator then describes to us not only the moon, but what looks like a "great ape," then the wind and the darkness, and finally the "creature" seemingly lifting its head.
At this point, Golding is limiting the omniscience of the narrator, showing us the creature as it appears in the darkness to the boys without telling us what it really is. This keeps us in suspense about the nature of this being.