The speaker is grieving someone who has died and wishes, painfully, to understand them. The opening admits a failure: no matter how hard they try, they cannot read the dead person's mind. Yet the mind seems almost on display, "open like a book" and "spread across the sky." The loss feels both vast and unreachable.
The speaker finds traces of the person everywhere, but only in their own "beaten heart," which suggests how worn down by sorrow they are. They try to bring the person back like a phoenix, though the image rises from "ashen lips," so the hope is already burnt out.
The last lines carry the main idea. After death, the person's words become braille, a language read by touch. The living, even those who can see, can't make sense of it, while those beneath the earth can. The mood is quiet, sad, and resigned: the dead still seem to be speaking, but the speaker is shut out from understanding them.