By understanding these three things, one may understand one s self. Understanding is the first step toward becoming a better martial artist or simply a better human being. This quote maps to the three things quite well. Of course, the three are capable of much more.
Taoist philosophy describes the body according to the first two treasures jing and qi.
Jing is a measure of the state of one s body. If one has a large amount of jing, then one has a good state of body. Likewise, if one has a small amount of jing, then one has a bad state of body. The state of one s body dictates what one can do with one s body. Thus, a small amount of jing yields respectively small body functionality while a large amount yields large functionality.