Blood on the Doorposts 
Each of the details that surround the Exodus from Egypt are instructive for all times. They are particularly significant for our own day and age as we look for ways to bring an end to our exile by recreating the dynamic forces of liberation unleashed at the time of the Exodus. When an event associated with the Exodus occurs in close proximity to the physical departure from Egypt, it is even more relevant to our own situation.
In the process of Redemption there are two components: that which G‑d does for us and that which we do ourselves. The relevance of any event in our Exodus is magnified when it involves action by the Jewish people. And any aspect of the Exodus that involved the actions of the Jewish people in close proximity to the Exodus warrants even closer examination.
The Door: Symbol of Freedom
Let us try to fathom the deeper significance of the sprinkling of blood on the doorposts of the Jewish homes on the night of the Tenth Plague, when the Death of the Firstborn Egyptians occurred.
The Torah teaches us that when a Jewish indentured servant completes his six year term of service but insists on staying a servant, the Torah requires that the master bore a hole through his ear and into the door.
The Jerusalem Talmud (Kiddushin 1:2) asks, “why the door? Because it was through the door that they [the Jewish people] went from slavery to freedom.” The Jerusalem Talmud obviously refers to the doors  marked by the ritual of sprinkling blood on the doorposts on the night of the Exodus. The door thus acquired the symbolism of freedom.
The servant who insists on remaining in servitude to another human being evidently fails to appreciate the value of and imperative for freedom. To underscore this lesson of the importance of freedom, he gets his ear bored to the door.
Freedom is not a right it, is an obligation. Although there are times when we must surrender our freedom for an overriding purpose (e.g., a thief who cannot make restitution, we must never allow ourselves to become career servants. The concept of servitude is only desirable when it is service to G‑d.
But Why the Door?
We must try to understand why the door, of all physical objects, symbolizes freedom.
It is interesting that the very same consonants which spell door in Hebrew “deles” can also be read as “dalus,” denoting poverty. What connection can we find between poverty and a door? And how can we reconcile the ideas of poverty and freedom, as they appear to be antithetical states of existence. A poor person is always indebted to others. Proverbs (22:7) says as much in the verse “the borrower is a servant to the lender.” It is poverty that forces a person into servitude. Yet, the very same word root that expresses the idea of freedom from poverty can actually mean poverty itself!
The truth is that deles has two opposite meanings. On the one hand it means poverty and on the other hand it means to be uplifted. It is both poor and rich.
The Poverty and Wealth of Speech
Chassidic literature applies this duality to the Divine attribute of Malchus, the Divine power of speech responsible for Creation. Our own human gift of speech derives from this Divine power of speech.
Speech is simultaneously the poorest and richest of all of our faculties. On one hand, Malchus or speech is represented by the metaphor of the moon, which has no light of its own. It is utterly poor. Words on their own are just scratches on a piece of paper or mere sounds created by a mechanical movement of our vocal chords.
But speech also is a medium that can carry the richest ideas and sentiments and transmit them to others. Speech, like the moon which reflects radiant sunlight, can reflect profound wisdom and powerful emotions.
This is very much like a door. The door blocks an opening in the wall and serves as a barrier for anyone who wishes to enter or exit. But simultaneously the door can swing open and allow traffic to flow through the wall in both directions. It both obstructs and facilitates movement.
We can now understand how the door, and the power of speech it represents, has become the symbol of freedom.
Pesach: The Freedom of Speech
The great Kabbalist, the Arizal, explains that Pesach marks the freedom of speech. The word Pesach is a composite of two words peh sach, which means the “mouth speaks.”
When we lose the art of communication, when we cannot express ourselves through speech, we are truly in a type of exile. There can be two ways of understanding the state of exile associated with one’s inability to communicate due to psychological and spiritual impediments, rather than physical causes.
First, it is obvious that a person struck dumb cannot relate well to the outside world. Without proper communication skills one cannot have a meaningful relationship with others. The speechless individual dwells in his or her own cocoon. The lack of communication creates an invisible but powerful “electronic fence” that keeps others out of your life and you out of theirs.
That is prison or exile at its worst. A human being is distinguished from all other creatures by his ability to speak. Whenever our Sages describe the four levels of existence (inanimate, vegetative, animal and human), the term used to describe the human being is midaber, the speaker or communicator. One’s compromised ability to communicate is a direct challenge one’s very humanity. In other words, the inability to communicate adequately places one’s humanity in a particularly disagreeable state of imprisonment. Even a physical prisoner is freer than one who cannot verbalize ideas and feelings. The former’s body is behind bars, whereas the latter’s humanity is behind bars.
Second, frequently the person’s inability to communicate with others can be a sign that he or she is not in touch with his or her own feelings. In other words, they cannot even communicate with themselves. Our Sages say, “Speech is the pen of the heart.” But if our hearts are dulled, and our feelings are muted, then there is nothing to express.  
To communicate with and care about others, we must be able to communicate and connect with ourselves. Communication is not only saying words to another; it is also a form of self-expression. If we have lost touch with ourselves and we no longer know who we are, how can we truly communicate with one another? What can we express other than superficial banter and banalities?
One of the deplorable characteristics of Galus is that many people do not know who they are and what they’re really all about. Their personality is a mystery even to themselves and therefore their whole being is in an internal exile. This is so whether they suffer from low self-esteem or from an inflated sense of self. Either way, they don’t really know who they are. This wretched state is what the prohibition of eating, benefiting from and owningchometz-inflated dough during Passover, discussed in this week’s parsha, is all about. If we want to be free, the fundamental message of Pesach, we must not suffer from self-delusion.
The key to true freedom is thus the ability to communicate with others, which in its turn hinges on the ability to be in touch with oneself. 
The Mezuzah as Symbol
We can now better appreciate the Mitzvah of placing a Mezuzah on the doorpost of our homes. This act is modeled on the sprinkling of blood on the doorposts of our Egyptian homes before the Tenth Plague.
According to Maimonides, the Biblical requirement of affixing a Mezuzah applies only when there is an actual door in the entrance as opposed to an open passageway. What is the spiritual rationale for this requirement?
Nachmanides writes (Commentary on the Torah, end of this week’s parsha) that the Mezuzah and Tefillin are both signs of the Exodus. Tefillin contain the section of the Torah that discusses the need to remember the Exodus. But how is the Mezuzah a remembrance of the Exodus? There is absolutely no mention of the Exodus in the Mezuzah parchment!
By now it should be clear that the Mezuzah on our doorposts is indeed a dramatic expression of true freedom; it symbolizes the unfettered power of speech represented by the door metaphor. Moreover, it represents a power of speech consistent with the ideals contained within the Mezuzah; particularly, the idea of G‑d’s unity.
Every time we pass the Mezuzah it reminds us that we need to have our own “door” (read: power of speech) influenced by the unity of G‑d as contained in the Mezuzah. When an awareness of G‑d’s unity defines our home, our lives and our speech, we are no longer in an internal prison. We know who we are and our rightful place in the cosmos. That awareness is the catalyst to our complete Redemption, whereby external and internal freedoms merge.