How we cite our quotes: (Book.Chapter.Paragraph)
Quote #1
He kept his eyes intently fixed on the Bohemian, and while the lively girl of sixteen danced and whirled to everyone else's delight, his reverie seemed to become more and more gloomy. At times a smile and a sigh would cross his lips, but the smile was by far the more pained of the two. (II.III.8)
You know that moment toward the end of the book when Frollo is staring at Esmeralda's corpse and he's compared to the spider with the fly? Think of this as something like foreshadowing. Esmeralda is young and lively, while Frollo is the opposite: prematurely old and gloomy. We get the sense that his gloom comes from the knowledge that he will never be able to get someone like Esmeralda. You could say that this is where all the evil starts.
Quote #2
"One fixed idea haunts me and pierces my brain like a red-hot iron." (VII.IV.23)
One aspect of Frollo's lust is his obsessiveness. It's something we've seen before in him, when it comes to his more-than-casual interest in alchemy. Frollo seems to be a guy who takes things to extremes—unlike, say, Phœbus, who doesn't choose to think too much.
Quote #3
He, who carried his heart in his hand, who observed no other law in the world but the good law of nature, who let his passions run off by his inclinations, and in whom the lake of powerful emotions was always dry, so assiduous was he every morning in making new channels to drain it—he did not know how furiously this sea of human passions ferments and boils when it is refused any outlet; how it swells, how it rises, how it overflows; how it heaves in inward convulsions till it has broken down its dikes and bursts its bed. (VII.IV.31)
Who says that Freud invented the idea of repression? This passage gives us some explanation of Frollo's dramatic behavior when it comes to lust. He might convince himself that he's not susceptible to lowly human wants and emotions, but according to Hugo, being in denial only makes things worse. It means that when Frollo does eventually have to confront his feelings, he's going to have no way of dealing with them.