How we cite our quotes: (Chapter.Paragraph)
Quote #1
In a word, I wanted only one thing: given a powerful man and a dissatisfied woman, to search out the beast in them, and nothing but the beast, plunge them into a violent drama and meticulously note the feelings and actions of these two beings. (Preface, 5)
In the Preface, Zola states that the goal of his novel is to put a dissatisfied woman into contact with a sexually powerful man, in order to examine what happens next. He's really acting like he's mixing two chemicals together, and then watching them explode. (All while taking exhausting notes.)
Quote #2
She preferred to remain idle, staring, her thoughts vaguely wandering. Meanwhile, she remained even-tempered and easygoing; all her will was bent on the effort to make herself into a passive instrument, supremely compliant and self-denying. (3.23)
At the beginning of the novel, Thérèse is extremely unhappy with her dull life. She languishes away in a constant state of passivity, hiding her true feelings deep inside of her. Until she meets Laurent, that is. Spark, meet fuel. Boom.
Quote #3
Thérèse, living in this dank darkness, in this dreary, depressing silence, would see life stretching in front of her, quite empty, bringing her each evening to the same cold bed and each morning to the same featureless day. (3.25)
Thérèse feels stifled by the depressing atmosphere of the shop. The pressures of her environment are what will lead her to commit adultery. At least, in Zola's opinion. One could also argue that people commit adultery because they want to.