[kazinator]

I think, you cannot have unity in a musical work if there is something new at every turn which does not reappear in any shape or form. In the best music from the Baroque era, there is new material throughout a piece. Many passages introduce motifs that do not make a reappearance. Or make a disguised reappearance just once.

I think, you will be hard-pressed to find two identical bars in a Bach fugue, where all the voices are doing exactly the same thing that was heard before. Even if a recurring theme appears, it's in a different way. Blatant copy and pasting is basically anti-fugue. Fugue-fail.

[wizofaus]

I'd agree it's rare to have exact repetition of a whole measure across all staves in a fugue, but you can certainly write a fugue using an initial theme and nothing but copy & paste with pitch shifting. Which you couldn't do for, say, a typical solo piano work by Scriabin or Messiaen...