The sentence below comes from a book, “Music and Cancer.”


In this sentence, I can’t understand what the underlined part [“rests would be history” (pun intended),] exactly means.

When the writer says that "the rests would be history (pun intended),"

1. You (the reader) would know all the rest, that is, the song cannot be a song.

2. Because the writer said "pun intended," it would make a reader still think about the musical term "rest."

Am I right?

Because rests are silent, people often misinterpret these empty spaces as unimportant. But, imagine what would happen if a song was made up of only notes, and no rests. Aside from the fact that the rests would be history” (pun intended), there would be a wall of sound with no reference point or discernible backbone to the music.

For you to know, I somewhat understand what “pun” means. For example, I fully understand those puns in the following thread.

If the musical rests are not used, then the rests would be history (they would be historical entities, not current ones).

'...and the rest is history' is an idiomatic fixed phrase meaning 'and the result is well known': http://dictionary.cambridge.org/dictionary/british/the-rest-is-history
Thanks a lot, Mister Micawber.