The subject matter of the Advaita Vedanta of Shankara (the non-dual branch of Indian philosophy) is the true, real unity of all apparently diverse things; “from the one comes the many,” but the “many” only seem to “come from” the One. In truth, there is always, only the One.
“The whole of creation is the field of consciousness [expressed] in different forms and phenomena.” 
It’s often summed up in the statement: “All this is That.”
Maharishi Mahesh Yogi also taught that the entire Creation begins with, and is encompassed by, the opening sound of the Vedas — “Ah” (depicted above).
In Kabbalah, this is called the “Seder Hishtalshelut,” often translated into English as the “process of emanation.” Things are said to “emanate” from their Divine source, like lightrays “emanate” from the sun. In truth, the rays have no separate existence (as the Rambam might have said), or “substance” (as Spinoza might have said), from the sun itself.
This emanation proceeds by 10 “degrees,” called the 10 S’firot (or Sephiroth, etc.). Yet, the S’firot themselves are only varying degrees of expression of the unchanging, all-encompassing “Ein Sof.”
Rabbi Mosheh Cordovero (the “RaMaK”), who had mastered Halachah (Jewish law) studying under Rabbi Yosef Caro (compiler of the Shulchan Aruch and a master Kabbalist himself), said that until he began learning Kabbala, he was “as if asleep and pursuing idle thoughts.” 
He wrote: “Do not say, ‘This is a stone and not G-d.’ G-d forbid! Rather, all existence is G-d, and the stone is a thing pervaded by divinity.” 
He famously depicted the 10 s’firot as emanating one-within-the-other (from the “outer” to the “inner”), beginning with “Keter” (of which כ is the first Hebrew letter). Each subsequent name is indicated by its (Hebrew) initial:
Other Kabbalistic diagrams and illustrations depict the Divine emanation as a process that unfolds from the “inner” to the “outer.” [*]
The descriptions might seem to conflict. However, if we remember that these aren’t “empirical” illustrations of the process itself, but rather depictions of different ways that we can view (or conceive of) the process, we see what our teachers are trying to tell us: We can think of emanation as happening either way. In the end, both “outer” and “inner” only describe our own limited viewpoint.
Meditation, or contemplation, in Kabbalah/Hasidut, may begin on the “process,” but only insofar as it points back to the essential, unchanging divine oneness. As the Ba’al Ha-Tanya says, in truth, from G-d’s viewpoint, the “emanation” never took place. It only takes place from the “human” viewpoint. Contemplation of this ultimately produces changes in consciousness and spiritual growth.
All “this” remains, eternally, “That.”
I see real parallels with Vedanta; you might, as well.
All this being said, Rav Kook (or Kuk) extolled the contemplation of “emanation”:
“How beautiful is the mystical conception of the divine emanation as the source of all existence, all life, all beauty, all power, all justice, all good, all order, all progress. How great is the influence of this true conception on all the ways of life, how profound is its logic, what a noble basis for morality. The basis for the formation of higher, holy, mighty and pure souls is embodied in it.
The divine emanation, by its being, engenders everything. It is unlimited in its freedom, there is no end to its unity, to its riches, to its perfection, to its splendor, and the influence of its potency and its diverse manifestations. All the oceans of song, all the diverse torrents of perception, all the force of life, all the laughter, the joyous delights — everything flows from it. Into everything it releases the influence of its soul force. Its influence, its honor, its deliverance reaches to the lowest depths.
The innocent and luminous will of man has already embraced some of its splendor. He continues to ascend, and he elevates everything with him. Everything proclaims G-d’s glory: ‘The grandeur of Your Holiness fills Your creation; (yet) You are forevermore, L-rd’ .” 
Rav Kook’s quote from the psalms may be interpreted in two ways:
One is the simple way, which I did by inserting “yet,” to indicate that despite the creation, the Divine is eternal and unchanged (the fundamental kabbalistic/metaphysical irony).
The other interpretation would be based on the Kabbalistic use of the Tetragrammaton (4-letter Divine Name) which, in Kabbalah, represents the 10 s’firot that embody the process of emanation (the 1st s’fira, Ein Sof, is the source of the emanation but is itself unexpressed; the “yud” represents the beginning of emanation, the 2nd s’fira, Hochma; the “hey” represents the 3rd, Binah; the “vav”, the 6th letter in the hebrew alefbet, represents the next 6 s’firot, and the final “hey” represents the 10th, “Malchut”. 1+1(Y)+1(K)+6(V)+1(K)=10 — the first “1,” representing “Ein Sof” — the Infinite, which contains everything within it — being unexpressed, the underlined four digits correspond to the Tetragrammaton and the process of emanation).
Rabbi Cordovero (the RaMaK) illustrated that the process of emanation takes place within Ein Sof by making the Hebrew letter “Alef” represent the all-encompassing “Ein Sof,” and including the four letters of the Divine Name within it:
Rav Kook’s use of the psalm verse would then mean: Divine glory fills creation because the process of emanation is eternal, yet never becomes separate from G-d; G-d remains present in the things created.
The Baal Shem Tov may be using this in his interpretation of: “I have set G-d [YKVK] before me always.”  He means: I have set the “process of emana-tion” before me always; I look at everything as emanating from the Divine at this very moment; yet, it is still only the Divine that truly exists.
So, both are possible. Rav Kook, although a Kabbalist, didn’t write as Kabbalists often do — with a lot of technical terminology. He was more likely to convey his ideas in non-technical prose, however poetic.