This quote from Lao Zi, 老子，is roughly translated, "A great sound rarely makes noise, a great figure has no form."
What might is mean for your practice of internal martial arts?
When a Taiji Quan practitioner possesses a deep understanding of the philosophy behind the movements in the form then what is occurring inside their mind and body might not be perceived by the casual audience member. Some practitioners describe feeling a great sense of calm and unity with the universe after learning and practicing Taiji Quan. Some one viewing these practitioners might notice the beauty of the movements and the serenity expressed on the face, but they cannot see the profound philosophy that lies deeply underneath the exterior.
This is the art that cannot be taught, but learned by practice and understanding of the great philosophy that takes no shape and rarely produces a tone.