Sancta Simplicitas (Diagnosis)
“Oh, Paul, Paul - then the news is good?”
He felt a slight shrinking at her obtuseness. After all, she was alive (it wasn’t her fault), she was merely alive, like all the rest…. Magnanimously he rejoined: “Never mind about the news now.” But to himself he muttered: “Sancta Simplicitas!”[i]
"Holy simplicity" describes what Paul Dorrance thinks about Eleanor Welwood well - simple minded, stubborn and naïve. Even in the situation when Dorrance proposes to her, he is not convinced by her personality; moreover, he is annoyed by her obtuseness and does not want her to know about the diagnosis.
For further readings:
Origin of Sancta Simplicitas 1
Origin of Sancta Simplicitas 2 (German source)
Origin of Sancta Simplicitas 3 (German source)
[i] Wharton, Edith; Robinson, Roxana (2007): The New York stories of Edith Wharton. New York, NY: New York Review Books (New York Review Books classics). p.389.