Nietzsche recognized the prodigious accomplishment of the Greeks in at least two seismic insights: (1) that man was somehow capable of being cultured to become more than just another heteronomous "phenomenon" within nature, society or history, i.e. he could in the most exemplary or extraordinary of cases stand in some sort of parity with the ultimate principles that shape and drive and organize existence (which is as much as to say: the gulf between aristoi and douloi is as abysmal as the chasm between cosmos and chaos, between arche and hyle or principle and matter); and (2) that in man nature—in actuality culture—had managed to produce a true prodigy of timebinding self-mastery, "an animal that dared to promise" and to make itself live up to its promised responsibility. Modern behaviorism and economism and scientism have undereaten the foundations of all these normative accomplishments. All the spiritual and rational and cultural and philosophical achievements of premodern civilization had long ago become nothing more than a treasury of rhetoric for moderns to pillage and deplete. Culturally considered, modern "culture" is de facto a form of entropy or self-parasitism, a thieving or vampiric world-order that accomplishes nothing whatsoever in the domain of norms; on the contrary it bleeds this domain down to nothing, to pathos.
Nietzsche's realization was astute that modernity had abolished the very prospect of humanity as ancient culture grasped it as aristeia or nobility, or even as medieval Christianity grasped it in the form of spirituality. Modernity has, from generation to generation and from century to century, an ever-lowering ceiling of minimalist "humanity," an arrant folly of setting up the democratist "human, all too human" as if it could in any way serve as some sort of norm or standard. It is nothing but a quivering, quavering mass of pathos, a gross form of moral and spiritual and philosophical bankruptcy: it is one great complex of fault-lines across the superficial plaque of a veneer-culture, a mere mask of humanity over bestiality. That is what our programmatic war against aristeia ultimately means, the systematic abolition of "man" as well considered as an honorific or value-laden concept.
The essence of human spirit would seem to be something static to Buddha: if it has an internal imperative to become something else (something higher or more spiritual), what self-disequilibrium could it suffer from that could nonetheless still be considered spiritual in Buddha's eyes? Nietzsche sought to explain this imperative for self-acculturation, for achieving rational self-mastery, for spiritualization, for self-radicalization and self-sublimation, by means of a "Will to Power" far more comprehensive than moderns (with only the cheapest and most facile grasp of "power") can understand. As a philhellene Nietzsche perceives and respects what the Greeks took for granted, that "power" above all else must be self-reflexive, an expression of aristic self-moderation (their anti-hybristic ethos and its correlative contempt for idiotia): "power" to the Greeks is moral and philosophical and cultural and political authority because it expresses itself in the hardest thing of all for humans to achieve, self-mastery.