21: During the meal there would be very specific foods and an order in which things were to be done. Therefore Jesus words, besides being surprising by themselves, would have come as a bolt out of the blue. Of course, Judas would ultimately have betrayed Christ anyway. But, Jesus words set the ball rolling. He instigated the timing, knowing the importance of the next day, and his Father’s timetable.
22: Although the disciples were not always the best examples spiritually speaking, their sorrow here was genuine. At least, that is, for the eleven. It is easy to imagine how they felt. Their question is interesting. Apparently none of them denied being a traitor. In the case of the eleven, it seems they realized that Jesus might know about a betrayal before the betrayer knew. Though weak at times, none of them were traitors.