Adam Clarke on John 9:6

Anointed the eyes of the blind man - It would be difficult to find out the reason which induced our Lord to act thus. It is certain, this procedure can never be supposed to have been any likely medical means to restore sight to a man who was born blind; this action, therefore, had no tendency to assist the miracle. If his eye-lids had been only so gummed together that they needed nothing but to be suppled and well washed, it is not likely that this could possibly have been omitted from his birth until now. The Jews believed that there was some virtue in spittle to cure the diseases of the eye; but then they always accompanied this with some charm. Our Lord might make clay with the spittle to show that no charms or spells were used, and to draw their attention more particularly to the miracle which he was about to work. Perhaps the best lesson we can learn from this is: That God will do his own work in his own way; and, to hide pride from man, will often accomplish the most beneficial ends by means not only simple or despicable in themselves, but by such also as appear entirely contrary, in their nature and operation, to the end proposed to be effected by them.