Matthew 26:25

‘And Judas, who betrayed him, answered and said, “Is it I, Rabbi?” He says to him, “You have said.” '

At His words Judas the Betrayer looked at him, being no doubt not a little disturbed, and challenged Him saying, ‘Rabbi, is it I?' And Jesus replied, ‘It is you who have said it.' It was an indirect positive affirmation turning the question back on the questioner. He knew it because he was guilty! Now Judas could have no doubt that Jesus knew what was in his heart. But his heart was now hardened and he could not draw back. His question, as with the other disciples, is put in a form that demonstrated that he expected a negative answer. How could he do otherwise in a crowded room? But perhaps he had still hoped that he was undetected. Now, however, he knew differently.

It is noteworthy that in Matthew's Gospel Judas is the only one who is depicted as addressing Jesus as ‘Rabbi'. Matthew does not feel that he can put the word ‘Lord' on Judas' lips as he had with the other disciples (that may also have been a translation of Rabbi, ‘my Great One'). The word on Judas' lips is left untranslated from the Hebrew/Aramaic, possibly because Matthew is bringing out that Judas belonged to the old Judaism, to the Israel that was now rejected. He had not moved into the new. Was it Jesus' clear knowledge of his activities that now precipitated Judas into premature action? Or was the betrayal already planned for that night? We will never know. But from that moment Judas was doomed, for instead of breaking down in repentance he hardened his heart, and his opportunity had slipped away.