The book is a powerful study of delusion, fear, and fanaticism. It is strangely relevant to some of the problems in the world today. The disassociation many poorer people experience with our society as they grow older and the fear that we all have of the ultimate bogeyman - it is bad enough falling into the hands of a wicked person who knows that they are wicked, but to be at the mercy of someone who believes they are doing God's will produces terror. The "justified sinner" never stops: to tire of wickedness becomes a renunciation of God's work.
The children in the panel represent the short time allotted to us in this world. From the baby in the woman's arms along the road to the man in the foreground the distance is short. The man in bunnet is carrying a mirror in front of him. He cannot see his own reflection in the miror because of the angle, but you can see it. Therefore he is looking at yours. He is frightened by what he sees and the malevolent Gilmartin/devil is looking at him in disgust over his shoulder. Gilmartin is not afraid of your reflection in the mirror.
Without the mirror the man in the bunnet looks entirely normal. You would not suspect his fears and the disgust he feels directed towards himself.
The composition itself represents the deep dark chasm people can fall into in the process of their lives. Dark featureless walls rise up on either side and the turbulant sky which only exists in the mirror is like some stagnant pool of water.
The young girl represents the possibility of salvation: she is not looking in any mirrors. She is laughing stright in your face.
