John 9:33

(33) If this man were not of God.—His argument meets each of their assertions. His general assumption, admitted as a universal truth (John 9:31), had denied their assertion that this Man was a sinner. His conclusion now denies their assertion, “This Man is not of God” (John 9:16).

He could do nothing—i.e., nothing of this kind, no miracle such as this, much less this miracle itself.