Verse Three

...And while Lennon read a book of Marx...
This is about the Beatles music becoming political. Songs like "Revolution" (1968) (which actually mentions Chairman Mao) were much different then "Love Me Do" (1963). Many American adults thought the Beatles were bad for the American youth, especially after Lennon's remark in 1966 about Christianity. He said "Christianity will go. It will vanish and shrink. I needn't argue with that; I'm right and I will be proved right. We're more popular than Jesus now; I don't know which will go first: rock 'n' roll or Christianity." This started anti-Beatles burnings and such.

...The quartet practiced in the park...
The quartet was the Beatles (there were four, not including if Paul McCartney is really dead!) and the park thing is Candlestick Park, the place of their last concert. It was practicing 'cause their music would grow after they stopped touring (their first project after this was "Sgt. Pepper" which is considered the best album of all time).

Verse Four

...Helter Skelter in a summer swelter...
Charles Manson is one of the most dangerous cereal killers ever (his favorite was coco-puffs). In the summer of 1968, he massacred an entire family 'cause of the Beatles song "Helter Skelter," which appeared on the white album. He thought that the Beatles were warning America about the racial conflict and it was "coming down fast." He thought the Beatles were the four angels mentioned in the Book of Revelation in the Bible. Manson wrote the title of the song on the wall in blood after committing the murders. Also, he thought in "Revolution 9" that Lennon was saying "rise" instead of "right," thought the line "They need a damn good wacking" from "Piggies" was telling him to kill people and the "Hollywood Song" in "Honey Pie" was about him 'cause he lived near Hollywood. He was dropping too much acid and thought the Beatles were talking directly to him and told him to kill those people.

...While sergeants played a marching tune...
Sgt. Pepper, Beatles, 1967, recently named the most influencal album of all time. First ever concept album. First to have lyrics printed on the back. First to have a design on the protector of the record. Included an elaborate cover design and cut-outs. As far as the music goes, it had drug references in Lucy in the Sky with Diamonds, sitars, animal sounds and studio trickery. In the song "Being for the Benefit of Mr. Kite!" at one point in the sound the engineer was instructed to cut the tape into small pieces, scatter them around, then tape them back together. In "A Day in the Life" (which was banned from the radio 'cause of the drug reference line "I'd Love to Turn You On"), after the piano cords die out, there is a minute of silence, followed by a high pitched sound (by the request of John Lennon, especially to annoy the family dog), then a loop of Beatles gibberish to make the owners of the LP think that the needle had stuck! What was I talking about again?

...The marching band refused to yield...
The Beatles had some anti-violence songs that made protesters think twice about the way they were acting. "All You Need is Love" (1967) says there is a better way then violence, and in "Revolution" (1968) one of the lines is "But when you talk about destruction, don't you know that you can count me out." The Beatles were in no way pro-government (as seen in 1968's "Piggies," which is about Congressmen), but they were against violence.