The remains if the day made me think about life and death. And the sad things that people decide to attach their whole lives to. The realities they choose to delude themselves away from and the ultimately meaningless 'purposes' for which they think they exist. 
 The chief character is a butler. His career and purpose in life is to serve an English lord. But I do not mean that what I found 'sad' was his situation of being a butler. No, working in households at that time in England was just as, if not even more, respectable than most other professions out there. And becoming a butler to a personage so prestigious as Lord Darlington is a great thing indeed. A butler in a position such as that is privy to all manner of things. He moves in a world that is simultaneously plebian and aristocratic, and is an indispensable portion of the lord's household. The English aristocracy placed a lot of weight in treating their servants right and butlers would often be trusted confidants of their lords and ladies. They set a lot of store by doing things 'properly' and butlers were experts in what was proper, at times even more than their overlords. 
 No what I really found sad was this sense of reckless ambition that drives humans to exceed at one thing or the other in life without seeking balance. Career becomes everything. No room is left for soul searching. Indeed such introspection and effort directed at seeking truth and meaning with regard to the state of existence known as life is treated as secondary to living life itself. This is akin to proceeding ahead with the game without knowing the rules, the playing field and most dangerous; who is watching. This to me is Ishiguro's central theme. It might not have been exactly what he intended but you know, the eye of the beholder and all that. 
 Lord Darlington was a real historical figure. And the rise and fall of the real Lord Darlington is central to the rise and fall of the self esteem of his fictitious butler. Along with the rise and fall of the prestige of the British empire. The prim past of a deluded colonial age. Given to grandiose self notions while that same self pillaged its vast empire with impunity, but they never saw things like that. No, to them this was God's work. And they imbibed themselves with all the righteousness it took to strut like cocks on increasingly thinning ice. Remains of the Day is about that ice gradually beginning to give way.