Suzuki writes in Zen and Japanese culture that the wielding of the sword does not mean just striking down the opponent, but it is concerned with the working of the Tao and the harmonious cooperation of yin and yang in cosmological movements. (p 150)
Tao is reached when one's mind is entirely emptied of delusive thoughts and intriguing feelings. (p 151)
The delusive mind is an intellectually bifurcated state of consciousness. The original mind is a mind unconscious of itself, whereas the delusive mind is divided against itself, interfering with the free working of the original mind. (p 110)
Both Zen and the Sword’s Way are one in that both aim at transcending the duality of life and death. (p 126)
These are all helpful when considering the question asked in the notes for Lesson 6, "Buddhism is a religion of compassion, so how does Zen activate the fighting spirit of the warrior?"
There seems to be some foundation for the explanation of the seemingly contradictory relationship between Zen and the Way of the Swordsman the experience of satori and the manifestation of the original mind in the following lines from the Sutta Nipata:
And then I saw
Whatever things are tied down in the world,
While it is doubtful that Sakyamuni would've accepted, advocated or even justified the Way of the Swordsman, we can see a connection here between the application of Zen to the Way of the Swordsman and the original stratum of the Dharma represented in the discourses of the Pali canon.