It’s the old “these dudes are crazy, let’s get outta here” trick.
One thing that comes to mind about the whole battle trance thing is the Scandinavian berserkers.
Another thing is that sung poetry is a very common way to remember and pass on knowledge in a illiterate society.
“Another thing is that sung poetry is a very common way to remember and pass on knowledge in a illiterate society.”
Yes it was an essential element.