Religious insight through a tumor (situational irony)
It is ironic that Sister John's religious visions are actually caused by a physical disease, because the visions appear to transcend bodily reality in spite of actually being the result of a bodily abnormality (i.e. a tumor).
Access to faith through a medical procedure (situational irony)
One might see it as ironic that Sister John must undergo a medical procedure (the removal of the tumor) in order to truly feel faith, since faith is typically thought of as being independent of science.
Sister John's initial selfishness about her relationship with God (irony)
It is ironic that Sister John, a nun, was selfish about her relationship with God for a long time (with respect to her special visions), since the act of being a nun is supposed to be selfless and nuns are meant to be humble before God -- yet the very way in which she went about being a nun was selfish.
The boyishness of the policeman (situational irony)
We expect authority figures, such as policemen, to behave as competent adults; it is therefore ironic that the policeman in the story seems like a little boy who is only pretending to be a policeman.
