Charles Ellicott Commentary John 10:21

"Others said, These are not the sayings of one possessed with a demon. Can a demon open the eyes of the blind?" — John 10:21 (ASV)

Others said, These are not the words of him that hath a devil.—We trace here again the presence of the better party among the Sanhedrin, which we found before (John 9:16). “His words,” they would say, “are words of calm teaching. The possession by a demon disorders, frenzies, makes the slave of madness. It is inconsistent with words like these.”

Can a devil open the eyes of the blind?—“Surely a devil cannot open the eyes of the blind?” is the form their question took. They go back from the teaching to the great sign which gave rise to it, and they find that work and word are alike opposed to the thought of being the result of a demon’s presence. Such a miracle had never before been known. A demon does not give the power to do a prophet’s work. (Compare to Notes on John 9:16 and Matthew 12:24.)