I would ask for a Biblical source for this assertion, but I know I'd never get it.
What are you disputing? That angels are pure spirit, or that pure spirits can only engage in intellectual combat?
Do you need a Biblical source to draw inferences? What is so hard to understand about what he said there? Does an angel have a body? And if not, how can it possibly be said to fight?
Sheesh, it’s a wonder some of you put your pants on in the morning without a Bible in your other hand.
After I posted that, I regretted being so sarcastic. Should have made the same point without being so ornery. My apologies.