It’s to show that one mistake in the game or rather one move that isn’t a check in the game from your side will result in a mate from your opponent. Nice puzzle btw :)
It is a sacrifice motif puzzle.
@YoBot_v2
By the way, how to defend in that situation?
Continuously check your opponent till a mate. Not a single move in which you don’t check your opponent. It’s a tsume. Yup sacrifice might be a good motif.