John Chrysostom — as excerpted in the Catena Aurea on Matthew 12:1-8

“To clear His disciples, He brings forward the instance of David, whose glory as a Prophet was great among the Jews. Yet they could not here answer that this was lawful for him, because he was a Prophet; for it was not Prophets, but Priests only who might eat. And the greater was he who did this, the greater is the defence of the disciples; yet though David was a Prophet, they that were with him were not.”