The Einstein-Cartan equation as the "living heart of gravity"? I recently read in A Journey into Gravity by Wheeler that

"The Einstein-Cartan equation gives us the most vivid image that mankind has ever won of the living heart of gravity" (P.118)

Unfortunately I was unable to find any more information about this. Does someone here understand what he means? 
What exactly does he mean be the Einstein-Cartan equation and why is it so important?
(I understand the basics of general relativity and the Einstein equation)
 A: A Journey into Gravity and Spacetime is John Wheeler's attempt at a popular yet comprehensive explanation of general relativity. He tries to convey all of the significance and depth of GR without using any mathematics beyond simple algebra and geometry. The explanations are very original and can sometimes be quite hard to follow and relate to GR as it is usually expressed (in terms of tensors, etc.). 
I'm no expert on GR at all--I am studying it at an introductory level for a master's course. I was wondering about this "most vivid" equation myself as I'm writing a paper on this book. 
In the section of the book that Wheeler says this, he is talking about conservation of "momenergy" (this is momentum and energy combined in the same way that space and time are combined into spacetime - i.e. momenergy is the momentum and energy 4-vector). Specifically, he is relating curvature to momenergy content. The word equation that precedes this quote is: 

(sum of moments of rotation for the faces of a little 3-cube) = 8π * (amount of momenergy within that 3-cube)

The 3-cube he is talking about is any one of the eight cubes that make up a tesseract 
dxdydzdt.
Looking through various higher-level GR textbooks and online sources, I tried to find an equation that relates curvature (on left side) to mass/energy/momenergy (on right side) probably with the constant 8π (though different choices of units may negate this part).
Is it just a rephrasing of this form of the Einstein field equations?
$${G_{\mu\nu}}={\frac{8\pi G}{c^{4}}}{T_{\mu\nu}}$$
Browsing further through Gravitation by Misner, Thorne and Wheeler, I came upon some sections that may be relevant: 15.4, 15.5, and 15.7, especially equation (15.28): 
$${G^{\sigma\tau}}=8\pi{T^{\sigma\tau}}$$
which is another version of Einstein's field equation, that Wheeler has called "the Einstein-Cartan equation" in G&ST for some reason (no one else seems to do this). I believe these sections of Gravitation correspond to the part of Gravity and Spacetime we are talking about.
In any case, just after the original quote, he says "Here glitters in a simple geometric form Einstein's 1915 battle-tested and still-standard law of geometrodynamics, his famous field equation."
This version is framed in terms of Cartan moments of rotation, as described in Gravitation above.
