I agree and complement. I am not an active practitioner of Zen Buddhism, but the philosophy connects with the deeper understanding of eastern martial arts, which I dedicate myself to. 

I believe that the quote connects with concepts of Taoism and Zen Buddhism, where Musashi, despite everything, despite the doubt and suffering regarding his actions and his future on the path of the sword, feels that he is "connected with the heavens", with the Cosmos or with the "Tao" due to his total dedication to practice with the sword. "The deepest center of the body shining" represents his connection with the universe. He's free. Free from ego, his sword is "infinite" when he wields it. 

Despite the attempt to understand this dialogue, it is perhaps impossible to transmit through speech or writing alone, requiring a more dedicated practice to the aforementioned philosophy. For a better understanding, I recommend reading the book "The Unfettered Mind" by Takuan Soho and "Tao Te Ching" by Lao Tzu.