Right after we recite “Hear O Israel! G-d our L-rd is one G-d” we say the following: “Blessed be the Name of His Kingdom’s Glory forever and ever”. As we’ll see, the latter isn’t from the Torah and actually predates it, as it was first said by our forefathers, and it had been reiterated ever since by the angels, as Moses encountered when he received the Torah (see Pesachim 56A, Devarim Rabbah 2:36).
Now, while we accomplish all that we said we do when we recite “Hear O Israel! G-d our L-rd is one G-d”, we fulfill even more when we proclaim “Blessed be the Name of His Kingdom’s Glory forever and ever” as we’ll see. But we’ll have to review a few things beforehand to understand its significance.
As we’d said before (see all of 2:5), though G-d uses an intricate, multihued, and circuitous control-system to interact with us moment by moment which oftentimes confuses and overwhelms us and conceals His presence, He Himself is surely behind each and every element. And we’re taught that the point of it all is to bring the entire universe to true perfection.
Thus, the one G-d has ironically deemed it necessary that His one goal be achieved through a multitude of intermediaries that must all submit to His single will. (It also follows that all those intermediaries are nothing more than extensions of His will, despite appearances, and that they’re means by which we can draw close to Him, much the way one could get close to someone important by knowing his confidants or the way the important person does things.) And when we recite “Hear O Israel! G-d our L-rd is one G-d” we not only affirm what we said before about G-d’s sovereignty, but on a deeper level we also affirm our faith in the fact that all of those intermediaries depend on G-d’s will alone, as well as our belief in the eventual arrival of universal perfection.
Now, that’s how things are in the broadest of terms. When it comes to humankind, though, we’re taught that in the ultimate future G-d’s name will rest on us and that we’ll then adhese onto His holiness; and that once that happens, His rule over humankind will be utterly manifest, and everyone will draw to Him and achieve perfection accordingly. G-d’s overarching aims would have been achieved thusby, and His Glory (i.e., His honor and renown in the universe) will be augmented.
But as we all know only too well, G-d’s Glory is not manifest now, inasmuch as His presence is largely hidden from us as a consequence of our sins and misperceptions. Nonetheless, the angels and all the other spiritual entities encounter G-d’s Glory all the time already, being pure and holy. His name rests upon them all the time, they adhese onto Him, and they’re always drawn to Him. And G-d’s Glory is thus in full bloom in the heavens. Thus they praise G-d with the words “Blessed be the Name of His Kingdoms Glory forever and ever” all the time, because His Glory is manifest to them, while humankind as a whole isn’t privileged to utter that.
But as we indicated above, our forefathers were aware of the significance of this statement (as well as of G-d’s sovereignty). And Jacob uttered it on his deathbed, as he achieved the status of an utterly spiritual entity. Thus while we don’t actually merit reciting it, we do proclaim it everyday when we recite “Shema Yisroel”. But we say “Blessed be the Name of His Kingdoms Glory forever and ever” in hushed tones, so as to concede to our less-than-holy state now — though we’re granted the right to proclaim it out loud on Yom Kippur, when we ascend to the level of angels (which we’ll touch upon later).