Try to simplify Berserk's themes and qualities as simply as you can describe. What is the core philosophy behind Berserk?
I see the question as less of an elevator pitch to the uninitiated, and more a request to condense what Berserk "means" as much as possible. It's a tall order though, because there are MANY themes, all of them intertwined to facilitate a dramatic, fascinating story. And I think Miura is primarily concerned with telling a great story, with the philosophical lessons from it taking a secondary footing.
But to answer your question, I think Berserk is an analysis of the human condition. The essential qualities of human beings are writ large in apostles, making them monstrous, which isn't unlike a fantasy version of how power corrupts a person. With the God Hand, we see humans as distanced from humanity as possible, empowered to perform terrifying acts. And in a character like Guts, we see the range of possibilities in humans -- the good and the bad. It's also a very optimistic series, to me. Because as overpowering as the odds always have been against Guts, he still struggles, he still overcomes. He's the man who will rise up, holding a broken sword.
P.S describe a bit about yourself. When did you become a Berserk fan? How has your view of the manga changed over time as you built a better understanding?
Berserk is pretty much the only series I follow these days, and I started reading it in summer 1999. I've followed it episodically since July 2000 (ep 165 was my first Young Animal), when I launched this site. Before that, I watched many different series, but once I realized the depths of Berserk, nothing else held a candle to it, and most comics just fall flat for me. As for my view of the manga, my respect for it has only gotten greater over time. There's no one else out there doing the kind of work that Miura is.