Nathan Phillips’s review published on Letterboxd :
Unexpectedly dark, honest, unsentimental chronicle -- from Kathryn Hulme's novel -- of a wealthy Belgian woman sacrificing identity and forsaking temptation to join a convent. The film is long, slow, careful and detailed and completely immerses the viewer in the emotional plight of Sister Luke, brought to us in body and spirit by Audrey Hepburn in what might be her greatest performance; I consider myself a fan but had no idea she was capable of this. Fred Zinnemann and cinematographer Franz Planer successfully contradict the aesthetic beauty of Sister Luke's surroundings with the increasingly dire, lonely circumstances of her day to day life. Every decision made, every change dealt with, every disillusionment or shock or harrowing moment of personal recognition is felt completely by us with Hepburn, in what must be one of the most magnificent feats of identification achieved by a Hollywood film -- and the events that unfold are both impressively organic and truly fascinating, as well as quite believable. The finale -- stirring in its dead-quiet subtlety -- is sure to inspire spirited, fiery debate within most of those watching. I was completely blindsided by this film's quiet, moving beauty and wisdom; try to know as little as possible about what transpires and just take the arduous but often rewarding journey with this marvelous actress.