Difficulty Seeing Heaven (Symbol)
When Robert is contemplating murdering Blanchard, he looks up to Heaven but "there was a dimness over my eyes that I could not see" (104). This symbolizes his estrangement from God and the fact that what he is doing with Gil-Martin is not sanctioned by Heaven.
The Consequences of Embracing False Teachings (Allegory)
The novel may be an allegory in the sense that it is the story of a young man whose embrace of false teachings leads into sin, despair, and eventually death.
The Double (Symbol)
The constant symbol of the double or the doppelganger (e.g., Gil-Martin) is one of fragmentation, of a divided self, of id/ego, of a center that cannot hold, and of moral duality.
Gil-Martin (Symbol)
Gil-Martin is a symbol for the devil; even his name, which means "fox" in Gaelic, is an allusion to the Devil.
Motif
There is a motif of the watcher, the observer, and the voyeur: characters are always dogging the steps of another as they try to carry out some purpose, whether malevolent or noble.
