"The blue ray seats the learnings ..."

[third-density-being]

how do you understand this statement?

Always in given context

(39.10 -> 39.07 in second book )
Ra: I am Ra. This material has been covered previously to some extent.
Therefore, we shall not repeat information upon which rays dwell in first
and second density and the wherefores of this, but rather attempt to enlarge
upon this information.

The basic pivotal points of each level of development; that is, each density
beyond second, may be seen to be as follows: Firstly, the basic energy of socalled
red ray. This ray may be understood to be the basic strengthening ray
for each density. It shall never be condescended to as less important or
productive of spiritual evolution, for it is the foundation ray.
The next foundation ray is yellow. This is the great steppingstone ray. At
this ray the mind/body potentiates to its fullest balance. The strong
red/orange/yellow triad springboards the entity into the center ray of green.
This is again a basic ray but not a primary ray.

This is the resource for spiritual work. When green ray has been activated
we find the third primary ray being able to begin potentiation. This is the
first true spiritual ray in that all transfers are of an integrated
mind/body/spirit nature. The blue ray seats the learnings/teachings of the
spirit in each density within the mind/body complex animating the whole,
communicating to others this entirety of being-ness.

The indigo ray, though precious, is that ray worked upon only by the adept,
as you would call it. It is the gateway to intelligent infinity bringing
intelligent energy through. This is the energy center worked upon in those
teachings considered inner, hidden, and occult, for this ray is that which is
infinite in its possibilities. As you are aware, those who heal, teach, and
work for the Creator in any way which may be seen to be both radiant and
balanced are those activities which are indigo ray.

As you are aware, the violet ray is constant and does not figure into a
discussion of the functions of ray activation in that it is the mark, the
register, the identity, the true vibration of an entity.

In my own words: Neither Orange nor Green are "Primary Rays". To Primary Rays group Ra included Red, Yellow, Blue and Indygo rays (Violet is beyond this kind of divisions/classifications). As I udenrstand those are the most basic rays that reflects major steps in Ones evolution of Self.
I don't know why Orange ray is not included as primary ray. Green ray seems to be "optional" - in Serving to Self polarity there's no work in Green center (up to middle sixth density, where polarization is"integrated" into "lack of polarization" - I'm not sure how to express it differently). Green ray is "only" a "resource" for Spiritual Work - not condition of being able to perform this work at all. Work in this ray depends upon Choice of third density (as I understand it).
RA spoke of "activation of Green ray" as He/They is/are Sharing Knowledge of Serving to Others nature.

Now regarding Blue ray - RA said:

"(...)This is the first true spiritual ray in that all transfers are of an integrated mind/body/spirit nature (...)

- I think it may be understood as balanced energies in lower/primary centers - I think it also includes Orange center, since without it "triad" of red/oragne/yellow could not be properly balanced (again - those are only my thoughts). In other words work in Blue ray begins when Entity reaches certain point of balance in lower rays, as in some degree "complete complex" of mind/body.

And than there's this quote:

The blue ray seats the learnings/teachings of the spirit in each density within the mind/body complex animating the whole, communicating to others this entirety of being-ness.

seats - as I understand - as "resides within", as a property of this Ray.
Animating - "within the mind/body complex" - as it would be the force that allows existence/life to "unfold" consciously.
communicating - as the basic function of Blue Ray - communication, expression, conceptualization, verbalization, etc - of Self to Self (being able to name/label understanding of Self and express it), as well as Self to Other-Selves.
entirety - previously mentioned "mind/body complex" (as I understand it) which includes at this level (Blue ray) Spirit component/facet of Self.

Finally statement "each density".
This is very hard, since We have no idea how different/higher densities looks like/what conditions are in them. I can only assmue that in each density Entities works with rays of mind/body/spirit complexes - fact alone of "not being veiled" doesn't mean that One is without bias and possess all necessary resources to be balanced/purified/refined. In some, incomprehensible for Us at this time way, Those Beings are Working with Their rays/centers. Each density has a proper work for itself.

I'm afraid that's all I can Share - my understanding/analysis of given Knowledge.
I'm at very begining of this work and I have no experience of my own to Share, therefore above is only a result of Mind confrontation with Ra's Words.
Neverhteless I hope I was able to help You at least a little bit, so that You can go one step closer to Understanding You Seek.

Take Care