Here's the last...pretty difficult...i have translated kokoro as "spirit" because it made the most sense. Also note the alternate translations.

"When one’s spirit is stilled, all is revealed in the spirit of bu .
Apprehending and developing this spirit through natural form leads to true bu .
The way to a bu that is still (receptive?) is through getting rid of bad habits (obstruction?) and being diligent in your training.
The only way to the pinnacle of bu is to walk in mushin ."

There is another interesting term, "kyoshin", that i have translated as "still" or "receptive". "Still" would of course not mean "passive".
I'm a year into my udundi training, and the "natural form" is being drilled to me more and more. Dropping kamae is becoming much more common, and the command I've been getting most often is "relax".
I can't say I know if I have "walked in mushin" yet. Anyway, it is not something we actively try to achieve. I think Uehara's concept of mushin is mostly psycho/somatic rather than religious or philosophical.