A Person's a Person, No Matter How Small!
Size doesn't matter--whether you're as big as an elephant or as small as a speck, your life has meaning. The people of Whoville may be tiny, but just like the rest of us, they have lives--and perspectives--that feel very real to them, from the mayor's troubled son to the willfully ignorant Whoville council members.
There are many ways to look at this idea, of course. But my takeaway was that it's vital for us humans, like Horton, to concern ourselves with the smallest and most helpless among us, those who don't always have a voice. We must speak out for them and respect their needs. And if you're one of those people who feels small and unheard--like the Whos--well, yell louder and louder! Demand to be noticed. It's your due.