Sometimes bands go to lengths that are heroic and sometimes you don't even notice it. This song has that kind of greatness and subtlety.
Verses one and two are a regular sixteen bars with eight lines of poetry, but only lines two and four rhyme. Instead of rhyming with line six, line eight leaves off on a sort of ellipsis that then leads into the refrain ("Young girl Sunday blues/And all her sorrow"). There are only three chords, but the melody is beautifully constructed without any kind of regularity at all, lines ranging anywhere from five to thirteen syllables in length. This is surely impressive in itself, but the Airplane arranged the whole thing for two-part harmony.
The two verses heard at the beginning make for some compositional heft right away, but then there's a beautiful, modulating passage that leads the way back for verse number three, now pitched up a whole tone. With the higher key, the energy of the song is continuing to build, but then they let it come down ("Let yourself wander free and easy") with a reprise of the chord structure from the instrumental passage now used as a bridge, Balin and Kantner STILL singing in harmony and allowing the energy of this great thing to build one last time to the end.