In Taoist writings, this statement is clearly echoed. The Tao Te Ching posits that a person need not travel to far off lands to gain wisdom and insight, rather, the individual need just look outside his/her own window. Apropos of this, we find many techniques in the Chinese systems of internal and external martial arts given names that reflect nature in a broader sense. It may be Kung Fu's adaptation of animal movements; it might be the "Hands through clouds" of Tai Chi.
In the words of aikido's Morihei Ueshiba, this theory is explained thus: "If you perceive the true form of heaven and earth, you will be enlightened to your own true form."
But why does this theory matter at all?
I think, if we are to achieve harmony--Oneness--either within our own psyches or with an opposing person or force, the theory is invaluable. It explains balance on an all-encompassing level; it explains the inclinations of behaviour and motion.
In addition, meditation, and/or Qi practice, often harness the mental connections of the human mind and the energy of the natural world. As sources of qi, we may bring down sun energy or lunar energy into our bodies. (Often the sun or moon can be used as focal points of meditation exercises. A candle, a microcosm of the sun, may also be used.)
Likewise, as the planets move in a circular pattern, so do we maximize energy in a throw. The gravity of holding the moon in place is the same gravity we use in martial arts, and is even reflected in our molecular makeup.
The reverse of this theory is also true: by studying the self, we can learn the secrets of the universe.