Can anyone explain the King and his horse conversation in Bleach?

Shirosaki: Ichigo, think you can tell me the difference between a king and his horse?Ichigo: What?Shiro: And don't even think about giving me some kinda kid's riddle answer. "Because one has two legs and one as four" It's about the form, ability and then power! Almost like the two could've been the same existance at one point! But then the one to fight to rise to the top becomes the king! Whichever one is leftover becomes the horse, lending his power to the king! Now I ask you, what's the difference between the two!? There's only one answer.........INSTINCT!!!! A vital tool for someone who has power but seeks more! A vital tool for someone who wants to be king! With this, the user will naturally be drawn to battles, be drawn to more power!! And use such to mercilessly obliterate his enemies beyond any recognition!! Slicing them into pieces! Mangling them!! All of this brought on by an absolute raw hunger for battle!! Our skin is peeled off, our meat scooped out, bones crushed, nerves nullified! Every part of us chiseled down to our very core!! All in order to fully sharpen our killing instinct!!! Something you have no knowledge of! Your instinct is too obvious, too normal! You only fight with reason, and always need a reason to cut down your opponents!! Just who the hell did you think of attacking when your sword was vaporized!? See, this is why you'll always be weaker than me ICHIGO!! You must excuse me, Ichigo. You know I really have no idea where Zangetsu is, but there's no way I'll let a king weaker than me hop on my back and ride me around!! I won't tolerate that kind of coexistence! You are weaker than me, so I'm going to destroy you. And then I'll be the one and only king! Shirosaki: So it seems like you somehow still had something left in you. The instinct you needed......to seek out this battle. Well whatever, so you beat me in the end. I guess all that means is that I'll have to kill you....king. But don't you forget this.....there will always be a slight discrepancy as to which one of us is the king and which one is the horse. That means if you get even the slightest bit lazy, that's all it'll take for me to knock you off and crush your skull beneath my hooves!!