How we cite our quotes: (Part.Letter.Paragraph)
Quote #1
But then what use is softening her heart if you are not there to take advantage of it? (1.33.3)
The Marquise de Merteuil is skeptical of Valmont's decision to seduce Madame de Tourvel more with letters than in-person. She thinks he should appeal to her heart instead of her head, and that his choice to write letters will put him at a disadvantage. Keep in mind that the Marquise doesn't actually want him to succeed. One reason it's so easy to be infatuated with someone you only know through letters or online is that you can imagine what they're like and fall in love with that, even if it has nothing to do with reality. So maybe Valmont's on to something.
Quote #2
There's nothing more difficult in love than expressing what one does not feel – I mean expressing it with conviction. It is not a question of using the right words: one does not arrange them in the right way. (1.33.4)
When Valmont succeeds with his seduction, the Marquise accuses him of really being in love and not, as he claims, faking it. She doesn't believe you can fake being in love; she thinks it's too easy to give yourself away by saying the wrong thing. Hey, it worked for these guys.
Quote #3
If you wish to keep up with this correspondence you must train yourself to decipher my drafts, because nothing in the world will reconcile me to the tedium of copying them out a second time. (1.34.12)
These were the days before computers with their copy/paste features and (gasp!) typewriters. If you wanted to make a copy of a letter, you would have to write it out again with pen, paper, and ink. Valmont takes the care to send polished letters, but he won't be making extra copies just so his frenemy the Marquise can read his handwriting.