Musashi vs Yagyu Sekushusai

I need a proper explanation resource of the chapter 101. I don't seek any spoilers beyond this chapter. If all these say spiritual or mind fights will be understood later on, I don't need explanation either. It just didn't seem logical to me that fight. No one has the ability to manipulate anyone without talking. I think the message here is not something applicable to real life but more about to convey the idea of mastering the mind somehow. I also have more questions. There are some drawing I couldn't give any meaning. What happens in the top right of the first panel? There is a hand clearly but what is the thing that is darker? Is it about something that musashi's hand is incapable of moving? Does it represent an obstacle? What about the top mid of the second panel? I mean literally what's it about?