The concept of the mezuzah refers to it first appearance description related to the exodus of the Israelites from Egypt where they marked a lamb’s blood above their doors in order that G’d will pass over them.
There is a positive Jewish commandment to remember each day any time about the Exodus of Egypt. The mezuzah will help to remember each time by just watching it.
Usually are mezuzah small items. The idea was to create that item into an art object worth to put on the door post as an artistic object.
Design of a Mezuzah