Sentence:  All cathedrals, pontificalities, brass and stone, and outer arrangement never so lasting, are brief in comparison to an unfathomable <WSD>heartsong</WSD> like this : one feels as if it might survive, still of importance to men, when these had all sunk into new irrecognisable combinations, and had ceased individually to be. 
Meaning of the word marked with <WSD> tags:  The expression of a person's inner essence, underlying identity, and reason for existence.