The Book of Wind
In The Wind Book, Musashi talked about the other dojos' weaknesses and bad habits. He talked about every particular technique and detail that is not beneficial and merely offers false hope. It is easy to say that Musashi's intention is for the warrior to stand firm and brace-up against the wind. Whatever distraction is presented, the warrior must rely on his intuition and judge correctly without being swayed. The warrior need not worry. If he is complete, he will know what to do. This is the essence of the Wind Book.
The Book of Void
The Void is neither the techniques nor the weapons that a warrior possesses. It is not the army nor the fortifications that one can acquire. The Void is the strategy, the understanding of the Gate, compassion, quest for the truth, timing, and perseverance. Without it, your foundation (The Book of Ground) will crumble, you will tremble in fear (The Book of Fire) against your enemies, and your techniques (The Book of Water) will fail you - all that is here will never work. The warrior must follow all these steps - one step at a time, to be successful. The Void is within you and without. This is the meaning of The Book of Void.
I dedicate this to my Sensei: Tadashi Yamashita, September 18, 1993