Iggeret HaKodesh, middle of Epistle 20
The Alter Rebbe now goes on to say that when the radiation descends in the third manner, it is manifest only in creatures of the lowest order, those deriving from the Element of Earth, this Element being lower than the other Elements of Fire, Air and Water. And it is mainly within the physical earth that the Divine power of creating yesh from ayin is revealed. This power derives from the essence of the Ein Sof-light; it is primarily found in the encompassing light, and is revealed through the Kav, the inner light.
This becomes apparent in the ability of the earth to make things grow: the physical growth of vegetative matter from the spiritual power of growth found in the earth is a clear demonstration of yesh resulting from ayin. Furthermore, the earth reveals this power constantly: it constantly produces vegetation as yesh from ayin. In this it differs from all living things that were created during the Six Days of Creation. Unlike all living things which, once created, simply reproduce, the earth consistently continues to reveal its creative power of yesh from ayin.
Thus, though the radiation within the earth is merely a “radiation of a radiation of a radiation,” it nevertheless demonstrates G‑d’s creative power — because it comprises both the encompassing light, and the light of the Kav which activates the power of the encompassing light to create and animate created beings.
The Alter Rebbe also explains that the distinctive power described above was revealed specifically within the earth, because Earth is the lowest Element of all. For, as explained above, it is specifically at the lowliest level of creation that the “rebounding light” manifests the essence of the original illumination with superior intensity. Read more…….