I tremendously disagree with the following conclusion-it fits what a mystic does perfectly.
"His ordinariness is Chesterton's: he is a man of simple tastes who enjoys the simple pleasures. But he is also a shrewd, clever person endowed with extraordinary sensitivity and powers of observation. With this balance of traits, Father Brown is not a mystic, nor is he a very realistic portrait of a parish priest."

(Dale 94)