The center for the Soul matrix body is the 5D layer of the Lightbody which sets the patterns for our etheric body, as such it is called the Archetypal Body. During Soul embodiment the 5D archetypal body merges with the physical layers through the blue flame or blue chakra wave spectrum. When bringing in the blue flame wave spectrum into the physical layers, the Soul becomes increasingly focused within the body, shifting consciousness into the Soul frequencies. When the Archetypal Body is activated it acts as a Perceptual Bridge, between the 3D layers and 5D Layers, and this activates the Mentor function in the human Lightbody.
The Soul Matrix is the first spiritual triad of when a human being starts to connect and integrate the soul body energies and heart complex during the first stages of the process of spiritual awakening or spiritual Ascension. The entire soul body is made of three layers that interact together into a Horizontal Triad Body. Each of these layers, 4D, 5D and 6D correlate to the same Chakra, its colored wave spectrum and a dimension of time and space in the future. 
Session Transcript - In order for the Soul matrix to become merged into a triad and anchored in the physical body, this means the person's got to have 72 frequency sub-harmonics running throughout those layers. So the Guardian is saying that we got the first 36 running, now we are working on the next base 12; the 48, 60 and 72 Subharmonic Strings. When we get to the 72 subharmonics, this is when we will have built the horizontal triad shield for the entire three layers of the merged Soul body. And this is about anchoring the Perceptual Bridge, creating the higher mind or the Mentor Field consciousness that they're talking about. See Perceptual Bridge session.
Term first found: Page 104, HGS Manual