The identity of the differential

"The best students, learning of the Tao, set to work earnestly to practice the Way. Mediocre students now cherish it, now let it go. The worst students mock at it. Were it not thus mocked, it were unworthy to be Tao. Thus spake the makers of Saws: the Tao at its brightest is obscure. Who advanceth in that Way, retireth. Its smooth Way is rough. Its summit is a valley. Its beauty is ugliness. Its wealth is poverty. Its virtue, vice. Its stability is change. Its form is without form. Its fullness is vacancy. Its utterance is silence. Its reality is illusion. Nameless and imperceptible is the Tao; but it informeth and perfecteth all things."