“sit and beg” = There was little that a blind man could do in those days to earn a living except beg. Some beggars walked about and sometimes went from house to house; the invalids lay down and begged; but the blind sat when begging.

“Isn’t this the same man” The change in his eyes and his demeanor would affect his appearance, but that is not the cause of the difficulty of his acquaintances and neighbors in recognizing him; their problem is their inability to accept this (to them) unbelieveable cure.