The Mezuzah is closely related to the idea of Shalom Bayit (Home Peace). It’s said that it reminds us to leave behind what we bring from the outside once we enter our homes, in order to really connect with a different and renewed deeper energy.
The reason why it is generally hung in a certain orientation is also related to this idea: the fact that it is not placed in a vertical or horizontal position, but inclined, implies that all parties in the house need to give in and to “incline towards the other” as to help have an harmonious and balanced family life.
The mezuzah marks a Jewish home as a sanctuary, establishing the border between the outside and the inside. Each day, when we return to our homes and we see our mezuzah on the doorpost, we are reminded of the importance of peace and compromise. It makes us think on the type of home we want to create.