St. Thomas Aquinas Commentary On John 9:41

St. Thomas Aquinas, Commentary On The Gospel Of John, Chap. 9: “According to Augustine, this shows the meaning of the previous passage, that is, that our Lord was referring to spiritual blindness.  He says, If you were blind, you would have no guilt, because you would be running to the remedy. For sin is taken away by grace, which is given only to the humble: ‘God gives grace to the humble’ (James 4:6). But now that you say, We see, i.e., proudly thinking that you do see, you do not recognize that you are sinners, your guilt remains, i.e., is not taken away: ‘God opposes the proud’ (James 4:6).

Chrysostom understands this passage as referring to physical blindness.  The meaning is then: If you were blind, physically, you would have no guilt, because since blindness is a physical defect, it does not have the nature of sin. But now that you say, We see, your sin is clear, because while seeing the miracles that I do, you do not believe me: ‘Blind the heart of this people’ [Is 6:10].

Here is another explanation. If you were blind, i.e., ignorant of the judgments of God and of the sacraments of the law; you would have no guilt, i.e., so much [guilt]. As if to say: If you were sinning out of ignorance, your sin would not be so serious. But now that you say, We see, i.e., arrogate to yourselves an understanding of the law and a knowledge of God, and still sin, then your guilt remains, i.e., becomes greater: ‘That servant who knew his master’s will, but did not make ready or act according to his will, shall receive a severe beating’ (Lk 12:47).”