This is a very important letter and especially the word Echad .... One !
The key statement in the first line of the Shema is that "G‑d is One." The Talmud speaks about "lengthening" the way one says the word "One": Echad. "Anyone who lengthens Echad has his days and years lengthened."1 Chassidic teachings explain that this means thinking about, or meditating on, the inner meaning of the word.
The idea that "G‑d is One" means not only that there is one G‑d, but that G‑d and the whole of creation are only oneness. There is nothing apart from G‑d. Nothing exists outside of Him; everything that we perceive, every particle of existence, is nothing but a veiled manifestation of G‑d.
For this reason everything in the universe is totally dependent on G‑d at every moment. G‑d created the universe a long time ago, but He also continuously keeps it in existence. The Sages speak of a stream of energy emanating from the infinite essence of G‑d, making the universe exist. Were He to remove this life-giving force from the world, it would no longer be there.2 As Maimonides puts it: G‑d can exist without the world, but the world cannot exist without G‑d. With this idea in mind, one declares the Shema with all One's being.
http://www.chabad.org/parshah/article_cdo/aid/407093/jewish/Expressing-Oneness-The-Shema-Prayer.htm
This is also very good. These letters are all so important......
Oneness: (from Chabad.org)
You hav ea very good understanding of the depths of this language. We need only to keep looking and Eloheinu will show us new and amazing things "beyond what we could ask or imagine".
This is why I could not get very far in my Hebrew language studies since every single letter would send me off in different directions.... when I get to Chet and the word Echad I become lost in this concept of Oneness then travel the roads with the Baal Shem Tov and the other Chassidic Mystics back further and further in time .... at one point I spent years lost in Moses Cordovero's Orchard of Pomegranates .... these letters are bursting with Light.