The poem is built around one odd, vivid image: the dead "stone fathers" don't simply vanish but go on living as eggs. Something hard and finished, like a gravestone or an ancestor's memory, turns into something fragile that might still hatch. The title, "Incubation," picks up that idea of slow, patient warming.
The speaker seems resigned but not unhappy. "We must be content / to sit on change" suggests that our job is to wait, like a bird on a nest, until change settles into something we can tell. "Fables" works as a verb here: experience hardens into story. The last line is the strangest. Varnishing paper for books hints that those stories end up preserved and glossed over in writing, which may be a gain or a slight loss. The poem doesn't say which.
The mood is quiet, slow and a little mysterious. It feels like watching over something that can't be hurried.