The greek concept of arete seems to me to be the basic essence of the kshatriya dhamma. Arete means "being the best you can be" (brief discussion here).
I came across it while reading Dan Simmons' Ilium, where a nano-engineered Odysseus engages in a Socratic catechism with the new Humans. Arete in later greek interpretation by Plato and Aristotle is sublimated from the active concept in Homeric legend to the contemplative ideal by these gentle philosophers. I think the Homeric concept is a much simpler and more direct attitude to life. Odysseus (rather than Plato, caught in the turbulence of barbaric invasions of his own time) is better suited to the airing of this superficially primitive warrior ideal.
The Kshatriya concept of the Vedic times seems to echo the Arete. I suspect that the mythic Arjuna and Achilles would have little trouble in understanding each other's actions. Krishna, in the Mahabharata, exhorts Arjuna to do and not worry about the result. I think the kshatriya philosophy is to strive for excellence in every act, not for anything beyond the effort itself. Who decides the parameters of this excellence? We do.
I think we can get a bit lost in answering "Why?" beyond a certain point. Whether we choose to rely on the divine or the superman or anything in between, the arete attitude is more than useful in the success of our works, whatever they be. But this is easier said than done. Excellence in all acts is a difficult thing. In a world that seems to have been created to defy and ultimately vanquish individual human ambitions, all violate action is a conflict against nature. I am reminded of Ramdhari Singh Dinkar's words -
Jo Jahan Hai Chup Chap Apne Aap Se Ladta Rahe
Whosoever, Wherever, you be; fight yourself silently.