The sharp and observant eye of Jane notices that St. John is a character who is not at peace with herself. As she spends more and more time and Moor House, what she observes is a man who constantly drives himself to do his duty like one who is possessed. Although Jane is quickly able to form deep and meaningful relationships with Diana and Mary, she finds it much harder to form such a relationship with St. John. She cites the fact that he is always away working as one reason for this, but then goes on to add:
But besides his frequent absences, there was another barrier to friendship with him: he seemed of a reserved, an abstracted, and even of a brooding nature. Zealous in his ministerial labours, blameless in his life and habits, he yet did not appear to enjoy that mental serenity, that inward content, which should bet he reward of every sincere Christian and practical philanthropist.
This is a very shrewd observation. There is something that is restless about St. John, and this does not allow him to be a character that is fully at piece. With his restless energy and the way that he drives himself to go out and carry on his work even in the most inclement of weather, there is a sense of someone who is unfulfilled and has not yet found what they are looking for in life.