Synthesis
Synthesis is not experienced as putting things together in a
unified whole: this is the quality of the synthetic capacity the
mind. The Being capacity for synthesis manifests in the ability
to see the unity before differentiation. One does not bring two
things together; one simply does not see them as two. (The Pearl
Beyond Price, pg 172)

Personal Essence and synthesis
One can see from the perspective of the nondifferentiated Being,
the Supreme reality of the oneness of existence, that all aspects
of Essence are differentiations proceeding from this original
undifferentiated source. The Personal Essence is the synthesis
of all differentiated aspects of Essence... So individuation is
the integration of the results of differentiation. The incomparable
Pearl is the individuation on the Being level. It is a new synthesis,
which in a sense creates a personal Being from the impersonality
of the nondifferentiated Being. The capacity for synthesis on
the Being level belongs to another aspect of Essence-objective
understanding. (The Pearl Beyond Price, pg 171)

Synthesis and brilliancy
So experientially, the state of synthesis means a sense of no
gap. Nothing is missing. The way it is recognized in terms of
affect is a sense of completeness, absolute completeness. That “I
am complete.” Usually, we don't know what it means to be
complete. We have never felt being complete in a real way. Completeness
is a very unusual perception. To know it, one has to actually
be the aspect of intelligence, be the Brilliancy, and be it completely.
It is not, “I'm experiencing it, tasting it, feeling it,
using it,” and so on. No. That kind of experience means
there is a sense of incompleteness. The completeness happens
when the person totally settles into the actual aspect of Brilliancy.
The completeness cannot be described in words. It can only be
contrasted to other kinds of experiences. In completeness, there
is no need, no wanting, no desire, and no interest. There is
no movement and no impulse toward movement of any kind out of
the completeness because nothing is missing. There is not even
curiosity, no stirring at all in the mind. And completeness is
not a collection of parts but a seamless presence. It is a beingness
that is a sense of amazing purity and innocence, radiance and
brilliance. Its texture is a sense of smoothness, delicacy, exquisiteness
and brightness. A completeness that defies words, really. (Essence
of Intelligence, pg 299)