The man answered and said to them, Why £ herein is the marvelous thing. Lange translates, "With respect to this man, this is marvelous, to wit." The R.T. has accurately given the force of the γὰρ, the combination of γε and ἄρα, by the rendering "why?"
The "herein" is the ignorance which the Jews now profess of the Divine call and mission of the Healer. Their confusion, their obscurity, their vacillation, on such a patent fact is the marvel of marvels, almost more wonderful than the cure of his blindness.
That ye know not whence he is, and (yet) he opened my eyes ( καί not infrequently has the three of "and yet"—simple juxtaposition conveying a strong contrast; see John 8:55; John 6:70; John 7:4). The man rises into holy and eloquent wrath.
Their entire history, their principles of judging of a prophetic call, the whole modus of Divine revelation, ought to have shown that one whose simple will stood in such vivid juxtaposition with work which none but Almighty God could do, ought to have enlightened them.
"The blind man, finding he was argued with, grew bolder, and began to argue in turn; if he had not studied theology (say rabbinical casuistry and Mishnaic accretions to the Divine Law), he at least knew his catechism" (Godet).