How do the diction, irony, and suspense affect the short story "The Black Cat"?

All three of these elements contribute to the horror of this story, "The Black Cat."  In the exposition, the diction of the narrator is suggestive of an astute and sensitive  mind: " I was noted for the docility and humanity of my disposition."  He remarks upon the 'unselfish and self-sacrificing love of a brute which goes directly to the heart of him who has ...tested the paltry friendship and gossamer fidelity of mere man." Yet, in a grotesque turn of events, he kills both his wife and his cat. 

Later, the contrast between the diction and the action becomes more exaggerated, suggesting the arabesque of Poe:  grotesque irony and terror. The forces of good battle with evil in him until the horrific act, understated with ironic effect:  "But this blow [of the axe onto the cat]was arrested by the hand of my wife.  Goaded by the interference" he decides to kill her in his rage.  With grotesque calm he remarks, "This hideous murder accomplished, I set ...with entire deliberation to the task of concealing the body."  Calmly, the narrator chronicles the events following his wife's death and his confidence in his "guiltlessness" until in his "bravado" he knocks on the walls to prove their strength. In response is a "shriek, half of horror and half of triumph."  With suspense mounting, the wall is torn down, revealing the horror of a corpse and a "hideous beast."