What does a Mezuzah achieve?

I remember as a kid, following lunch on Rosh Hashana, I would meet with friends to blow Shofar for those who may have missed hearing it in Shule that day. We walked up and down many streets, always looking for Mezuzot that would identify a home as Jewish, before proceeding to knock on their door. 
Now as a Rabbi, I have affixed many mezuzot on people’s homes. Even those who observe hardly any other custom or observance, somehow find great importance in hanging a Mezuzah on their front door. 
What is the secret behind the Mezuzah?
The source of this Mitzvah is contained in the week’s Parasha Vaetchanan. In the very first paragraph of the Shema that we read every day, we recite: “And you shall write them on the doorposts of your home and upon your gates” (Devarim 6:9). Mezuzah literally means doorpost. The implication is that the scroll itself, and the Torah that it represents, should become a part of your very home, your doorpost. More than this, the words shall be inculcated into the very fabric of your existence. As the Talmud says (simple reading): “Ein Ish belo bayit”, you are not a person, if you don’t have a home. Somehow, a home is integral to being an “Ish” – a wholesome and integrated human being. And for this to happen the Mezuzah, the ‘soul’ of your home must be integrated into the body of your home, its actual physical structure. 
There is another explanation. The word Mezuzah is related to the source word ‘Zuz’, meaning ‘move’. The blessing that is recited upon putting up a Mezuzah is “likboa Mezuzah”, to ‘affix’ a mezuzah. What this means is that we must ‘fix’ our ‘movements’. We must ensure that the home that we build for ourselves is one in which we are constantly seeking to improve our behaviours and bring greater good into the world. A home that is based on the eternal jewish values that are contained in the Torah and in the parchment of that very Mezuzah. 
A final explanation. There is a heated debate amongst the Talmudic sages as to whether the Mezuzah should hang vertically or horizontally. What is the Jewish law? A compromise! We hang the Mezuzah on a slant. The message is this: Every Jewish home must be built on humility and compromise. It must be based on an understanding that we must make room for the other and learn to appreciate another opinion. Only such a home will last and will likely produce inhabitants that are upstanding citizens and worthy examples.
Wishing you all Shabbat Shalom and I look forward to welcoming you in Shule,
Rabbi Yossi and Chana Raizel Friedman