Yichuan YizhuanLine statement
The second and fifth lines form a proper correspondence. Even in a time of divergence and retreat, the second responds obediently to the fifth through centrality and correctness, while the fifth bonds intimately with the second through centrality and correctness.
Their communion is naturally firm. Yellow is the color of the center; an ox is an obedient creature; hide is a tough and firm material.
As the second and fifth interact in accordance with centrality, correctness, and compliant Dao, their bond is as secure as if tied fast with yellow ox hide. 'None can untie it' means that the firmness of their bond cannot be fully expressed in words.
Because it is a time of retreat, it is stated in the most superlative terms. The Xiang Commentary says: 'Bound with the hide of a yellow ox' means holding firm the will.
Above and below bind one another through the Dao of centrality and compliance; their wills are exceedingly steadfast, as if fastened with the hide of an ox.