The line is from Valery's La Jeune Parque. 'Le' cannot refer to 'ombre' since it is feminine. And I doubt it refers to some general thing such as 'reality' like in the sentence 'it rains'. So I'm basically clueless here. Here's the full context:
L'esprit n’est pas si pur que jamais idolâtre
Sa fougue solitaire aux élans de flambeau
Ne fasse fuir les murs de son morne tombeau.
Tout peut naître ici-bas d’une attente infinie.
L'ombre même le cède à certaine agonie,
L'âme avare s’entr’ouvre, et du monstre s’émeut
Qui se tord sur le pas d’une porte de feu.
And while we're at it, let's go ahead and tackle '
entr'ouvre because I don't get that either. Is 'ouvre' an adjective, preposition, what? I would think 'entre' would be the verb but hey maybe I'm wrong. It was translated as
The clutching soul half-opens and is moved but I don't think that is a literal translation.