Knowing the Way of the long sword means we can wield with two fingers the sword that we usually carry. If we know the path of the sword well, we can wield it easily.
If you try to wield the long sword quickly you will mistake the Way. To wield the long sword well you must wield it calmly. If you try to wield it quickly, like a folding fan or a short sword, you will err by using "short sword chopping". You cannot cut a man with a long sword using this method.
Go Rin No Sho (1645) - The Water Book