It is important to recognise that this novel is written in the first person, and so Jane is the narrator of the novel. This means the reader never actually finds out what St. John Rivers thinks of himself, because Jane only presents her perspective on her cousin. However, it is clearly possible to identify some elements of how St. John Rivers would view himself. Above all else he is a man who has set his face towards a particular destiny that he will carry through to completion. Note how he talks about his desire to be a missionary to Jane. He says how his father had opposed his desire to serve as a missionary, but since his death he has had little opposition:
...a last conflict in human weakness, in which I know I shall overcome, because I have vowed that I will overcome--and I leave Europe for the East.
The "will" in italics is important as it reveals his absolute determination and his unswerving nature. In the novel, all characters can be divided between those who are dominated by passion and those who are dominated by reason. St. John, as his association with ice and snow demonstrates, is a character who embraces reason and shuns any sense of passion, much to the chagrin of Miss Oliver, who is of course the "last conflict in human weakness" that St. John refers to. It is precisely this extreme reason that Jane finds so difficult to live with and leads to her refusal of her cousin's hand. By this time, Jane has learnt the value of a balance between the two extremes, and a future with her cousin would force her to erase any passion from her life just as he has done in his own life.