To me, the song has such a strong unifying structure that I'm having a hard time really isolating any individual verse from the others. It's almost like a three-point essay. Intro, three topic paragraphs, conclusion. It's also very deeply connected to a specific time and place in history, to me.
But if I have to choose, I guess I'll say verse 4. Something about young people taking the mantle from the previous generations and making the world they're growing into. And while that is always happening I think there was a particular flavor to the youth movement of the 60s that is captured in this song. I think about all those kids who ran away to Haight-Ashbury, believing they could change the world- and in some ways they really did. I wasn't alive then but I watched all the The Wonder Years episodes with Karen in them so I totally know.