He explains that the speaker's words are transformed into thoughts in the mind of the listener. The letters that make up the speaker's words, are become letters of thought in the listener's mind. This is true in our interpersonal interactions, and on a deeper level still.
Our own thoughts, the Pri Ha'aretz explains, are the words of the Shechinah. HaShem voices His desires through the Shechinah as letters that make up words, and those words, in turn, become letters of thought in our minds.
Through our awareness of this, he goes on, we can bring about unifications of the upper worlds when we connect the letters of our thoughts to the voice of our thoughts, the nikkudoth of the letters of our thoughts. In this way we unite the voice, with the letters, HaShem, with the Shechinah. Those who can understand the depth of this relationship can unite KB"H and His Shechinah with their every thought.
This is a tremendously deep idea which pushes the limits of things I understand well enough to explain. For us, the dichotomy of speech into letters and voice is an interesting place to stop and examine.
It's a fairly simple thing for us to be aware of how the raw sound of our voice is modulated and broken up into words. Right? We can sing a melody, or add lyrics and turn it into a song. Without the lyrics, it's just sound. With the lyrics, suddenly our voice is transformed in a profound way.
Yet to make the leap of understanding from words to letters is a little counterintuitive. The way we learn letters, we learn them as a system of recording the sounds of speech, not as integral components of that speech. In modern linguistic theory it's pretty clear that speech evolved first, and writing much later.
Think about it further, you have non-verbal speech (body language, mannerisms, expressions) that would clearly seem to predate both speech and letters. Yet, according to Jewish tradition, the letters precede speech. Letters precede communication. Without letters, there's no communication. Even thoughts have letters.
Let's try to understand this a little, what it might mean.
We all can think for a moment and understand that no matter how quickly we speak, each of our words is rooted in thought. We think something first and then let it out as speech.
If we look at our thoughts, in the modern scientific understanding, they are a concert of nerve impulses that somehow encode the state of some concsious awareness that we would eventually break down into individual thoughts. (there are a lot of ifs here, but for simplicity's sake lets say we can somehow, at least hypothetically, break down the flow of consciousness into disparate thoughts.)
Each of these thoughts is made up of the various neurons that are firing at the moment of that particular thought. If we thought of each neuron in our brain as a unique 'letter' of thought, then we could begin to describe the letters that make up the 'words' (groups of neurons that fire in tandem) of a particular thought.
So, we can begin to grasp the idea that every one of our thoughts, let alone every one of our words, can be broken down into component parts. Calling these parts 'letter's might seem a little far-fetched, but we're far beyond where we were before. We are no longer shocked at the idea that the components of our thoughts precede those thoughts. There is something we could call 'letters' even before we can begin to discuss speech.
For me, this jump is far enough. Once we recognize that our thoughts, and yes our words, are made up of something, anything at all, then we can start to understand what the Torah means when we learn that our words and thoughts are made up of letters.
Now that we can begin to understand our thoughts being composed of letters and how the words of the speaker become the thoughts of the listener, perhaps we can reevaluate a commonly held Jewish practice.
We are encouraged by many of the greatest Hassidic Rebbes, as well as by Halachah (Jewish law) to repeat certain ideas or passages of text to ourselves out loud. The most obvious example is the Shema Yisrael. When we recite the Shema or any other prayer out loud, we are basically reinforcing our thoughts by allowing our speech to reenter ourselves and further direct, underscore, strengthen and frame our thoughts.
The more general practice of reminding yourself of particular holy ideas out loud, and the fact that Torah learning really needs (l'halachah) to be read to oneself out loud, shows just how thoroughly Judaism embraces this idea.
In fact, in this context, perhaps we can understand Na'aseh v'Nishma -- we will do and we will listen -- in a new light: Through the doing, the act of speaking HaShem's Torah to ourselves, we allow ourselves to hear it more clearly. Repeating HaShem's Torah focuses our understanding and our heart so that we may truly listen to what HaShem is telling us.
Perhaps this also explains the first verse of the second paragraph of Shema Yisrael, "and when you hear, listen!" (והיה אם שמוע תשמעו)