Raja is right - if you are 'up in arms' about something it means that you are angry about something. I've had a look at the lyrics of this song, and to be honest, they aren't very meaningful. They are just words that sound nice. It means angry, but in the context of the lyrics it also suggests an embrace of some kind. Don't worry too much about the meaning - just enjoy the song!

up in arms is an idiom.. which means to get angry over something