I think that one of the most critical themes of Wharton's work is how friendship can move into the realm of vengeful rivalry with such ease. The process in which the friendship between the two women disintegrates is startlingly quick. An association that spanned decades is reduced to emotional rubble in an afternoon. While there might have been latent hostility between both women, it was subverted for the good of a friendship or association that lasted over a sustained period of time. Wharton's point in showing how quickly this relationship ends is reflective of how rivalry can destroy connective threads in less time than it takes to establish them. This theme of friendship and the weak foundation upon which it exists if it not properly nurtured is evident.
I think that another important theme Wharton illuminates is the presence of intimate cruelty. When we think of the works that display what cruelty means on a personal level, existing between two people in the realm of the intimate, one has to consider the afternoon between Alida and Grace as representative of this. The theme of cruelty is evident in how both end up wanting to hurt one another. Alida's anger gives way to her confession and Grace's response to it are both examples of how personal cruelty can be evident in many settings of emotional intimacy. Wharton is skilled at being able to evoke the theme of cruelty in the personal realm, showing how we are sometimes at our worst as a human being with people who deserve only our best.