How we cite our quotes:
But she felt very warm and often stopped to mop her face on which the perspiration gathered in beads. She unfastened her white sacque at the throat. (2.1)
This is a prelude of what's to come. Alcée's not even there yet but Calixta already feels hot and bothered. The gathering storm is making her "fe[el] very warm," and she's already sweating and starting to take her clothes off. Out of context, this passage could be taken pretty sexually.
Alcée clasped her shoulders and looked into her face. The contact of her warm, palpitating body when he had unthinkingly drawn her into his arms, had aroused all the old-time infatuation and desire for her flesh. (2.16)
Calixta's body reminds Alcée of the old days and the way he used to feel while holding her. There are lots of words here we could focus on, but let's go with "unthinkingly." Alcée is not thinking, at least not with his head. The body is totally in charge here.
Oh! she remembered; for in Assumption he had kissed her and kissed and kissed her; until his senses would well nigh fail, and to save her he would resort to a desperate flight. If she was not an immaculate dove in those days, she was still inviolate; a passionate creature whose very defenselessness had made her defense, against which his honor forbade him to prevail. Now – well, now – her lips seemed in a manner free to be tasted, as well as her round, white throat and her whiter breasts. (2.18)
Consider here how all these different languages – of imprisonment and freedom, love and chastity, honor and defense, and purity and violation – are used. In the memory, it's about honor and chastity – the words of courtly love. Calixta is an "inviolate" maiden, and Alcée is "desperate" in his "defense" against her "defenselessness." As that language of honor fades away, it's replaced in the present by much more explicit language about Calixta's body. As her body becomes "free to be tasted," it also becomes free to be described, in terms of her "white throat and her whiter breasts."