From Zhuangzi Chapter 3: life cultivation.
The quote is part of the butcher’s explanation to Liang’s king about how he cuts cow.
Between the joints is gap, but the blade edge no thickness. With no thickness entering gap, comfortable and relax – the swimming blade surely has space to play, thus nineteen years and the blade still like brand new.
(My own crude translation)
If the blade is self/ego and the cow our world.
How do you enter?
Are you still fine and sharp like brand new? Or are you chipped and dented and broken?
This is life cultivation.