You can create a new work subject to copyright incorporating other works. Any movie with music is an example, and so is “sampling” in music, or translations of books.

At issue here is wether the changes to the song were significant enough for it to be considered a creative work.

This is no different than the test for a de novo work:

    Echo „hello world“

Is not enough to trigger copyright protection. Yet the MacOS source code is. Somewhere between the two, there is a line of demarcation. Where exactly that line is was the subject of this lawsuit.

Most of those traditional church hymns are really old; many not subject to copyright or, those that are, simply no one cares. If the UU had to fight for them, some could be protected under satire/parody.

Relevant discussion recently about copyright and church songs (disclaimer - I wrote the first rant, and people contributed in the replies):

https://news.ycombinator.com/item?id=16227520