Albert Barnes Commentary John 9:28

"And they reviled him, and said, Thou art his disciple; but we are disciples of Moses." — John 9:28 (ASV)

Thou art his disciple. This they cast at him as a reproach. His defense of Jesus they regarded as proof that he was his follower, and this they now attempted to show was inconsistent with being a friend of Moses and his law. Moses had given the law respecting the Sabbath; Jesus had healed a man contrary, in their view, to the law of Moses. They therefore held Jesus to be a violator and despiser of the law of Moses, and, of course, that his followers were also.

We are Moses' disciples. We acknowledge the authority of the law of Moses, which they alleged Jesus has broken by healing on that day.