Expositor's Bible Commentary Commentary John 13:29

"For some thought, because Judas had the bag, that Jesus said unto him, Buy what things we have need of for the feast; or, that he should give something to the poor." — John 13:29 (ASV)

The reference to making a purchase for the Passover may corroborate the view that this Last Supper was held on the night preceding the Passover (cf. comment on v.2). Jesus would hardly have waited until this moment to obtain a lamb if they were at the Passover at that moment; and the text says that the disciples didn’t know the reason for Jesus’ statement to Judas, which would hardly be the case if the lamb was missing.