Well, considering this is an "autobiography" of Dunstan Ramsay, the main character role we need to be concerned about is Dunstan Ramsay. All of the other characters are only important in how they intrude upon his life. In short, Dunstan Ramsay sees himself as living in a world of contemporary saints (or, at the very least, people connected to the supernatural). Further, it is of lesser importance that he is a retired teacher.
Ramsay sees changes in many characters that leads him to believe that some people are saints in this world.
Because we love the saint and want him to be more like ourselves, we attribute some imperfection to him. ... If you think her a saint, she is a saint to you.
Further, these changes also get Ramsay interested in magic. For example, due to her interesting (and sometimes questionable decisions, like that of her decision with the tramp), Mary Dempster is considered a contemporary saint by Ramsay. The irony is that the use of the word "saint," while it originally makes the reader think of religiosity, is far from it. In fact, Ramsay is more interested in the connection with supernatural forces. He is always connecting one religion to another through different characters in their holy texts.
War changes Ramsay, who returns both scarred and wounded. Ramsay then reconnects with his "lifelong friend and enemy" newly renamed "Boy" Staunton. These two "rebirths" give them mythical and supernatural status in their own eyes. This status ends badly for Staunton who is finally convinced that he caused a tragic premature birth in his youth and kills himself as a result. Therefore, with a twisted sense of justice, Ramsay himself becomes a contemporary "saint."