As just one more point of reference for this song's cultural power: whereas the greatest movie about boxing, Raging Bull, made such wonderful use of highbrow music like the Intermezzo from Cavalleria, the greatest boxing movie, the first Rocky movie, in its own way, makes wonderful use of more familiar touchstones. In particular, an instrumental "Silent Night" plays jarringly in the background of the dramatic climax scene, where Adrian stands up to her brother. Masterful.

https://www.youtube.com/watch?v=fxriLTLhyyY