Why are Montresor's family motto and coat of arms important?

Montressors' coat of arms represented an eye for an eye leaves the world blind, something with two snakes.

A huge human foot d'or, in a field azure;

the foot crushes a serpent rampant whose fangs are embedded in the heel.

The motto is: Nemo me impune lacessit or No one provokes me with impunity.

Definition of heraldic terms: - d'or (should be Or): golden

- azure: blue

- rampant: (of an animal) rearing