长拳者，如长江大海，滔滔不绝也。
Translation:
Chang Quan, likes a long river or ocean, surges on forever, constant and never-ending.
Explanation:
This sentence tells us that Taiji Quan is called chang quan because there are many postures, and they can be practiced continually in long way.
I tend to read it as a quality of the art rather than a description of the forms!