Symbolism, Imagery, Allegory
Busted for carrying a bottle of brandy and unable to pay the fine, the priest ends up in a crowded jail cell. Feeling a strange companionship with his fellow prisoners, he tells the others there that he's a priest. He is struck with affection for them, as if they were his parishioners.
Here, in the cell, with only one stench-emanating bucket to share among them (Ew!), the priest sees himself as one criminal among others. Here, they are equal, united by some wrongdoing or other. The priest is not better than they are, as he thought before the time of the persecution.
He had once believed that being a priest meant a life of comfort, deference, and respect. The persecution robbed him of that notion, but it's in the exceedingly uncomfortable jail cell that he really begins to feel the meaning of his vocation. He's moved by "an irrational affection for the inhabitants of this prison" (2.3.77). He's moved to love as he believes God loves.
For the priest, the prison is a place of grace. It's the life of luxury that is truly most dangerous for him—a lesson he learns only after he has escaped the state and the police tracking him. About time he learned his lesson.