Note 6 at Joh 13:29: Although Jesus had very plainly revealed Judas as the one who would betray Him, His disciples didn't understand that Jesus was telling Judas to get the betrayal over with. What they understood Jesus to be instructing Judas to do is very revealing. They thought that Jesus wanted Judas to buy provisions for the feast or to give money to the poor.

This verse reveals that Judas was the treasurer for the Lord (i.e., Judas "had the bag," Joh 12:6). It also shows that the Lord, who no doubt knew that Judas was a thief (Joh 12:6) as well as the betrayer, didn't take this position away from Judas.

The disciples also didn't think it was strange that Jesus would send Judas out to give some money to the poor, even at night. Although there are no recorded instances of Jesus giving money to the poor, this certainly must have been a common occurrence to have the disciples respond in this way.