Essentially, it means "lead by example", "let others learn through acts and not words", "there are situations which no amount of skill can rectify", and "accept that some may not understand what you try to teach."
Asking what something means is effectively asking for a translation. Unfortunately, that's almost always a lossy process, and in the worst case it invites an "understanding" that's largely different than the author's original intent.
If intended meaning is something you'd like to get at, I've gotten a lot of mileage out of the question, "what mindset and situation would I have to be in such that those words come naturally, spontaneously to mind?"
Anyway, in my experience with lots of meditation, the sentiment expressed in OP's quote is something that feels close to home. I think it has more to do with staying close to the problem at hand and being keenly aware of how all the pieces of you fit into that picture.
There exists a mental space where you can do things and have desires while at the same time seeing a larger context that breeds equanimity. It's a space thst makes things like personal thoughts, feeling and beliefs seem as simple and matter-of-fact as crickets chirping in the night.
It means that everything will only change when you change yourself. Find your own harmony and don’t worry about others. Their path is theirs.
Some of these types of books say that yourself is the only thing which you can truly change because, they say, everything else is an illusion or simply that trying to change others is a futile task. How you perceive reality is everything.
I find this idea to be very liberating and pragmatic and when I remember to utilize this in practice, things flow much better for me. I become more flexible.
As Bruce Lee says - "You must be shapeless, formless, like water. When you pour water in a cup, it becomes the cup. When you pour water in a bottle, it becomes the bottle. When you pour water in a teapot, it becomes the teapot. Water can drip and it can crash. Become like water my friend."