Bede the Venerable — as excerpted in the Catena Aurea on Mark 8:27-33

“(ubi sup.) Wherefore He first asks what is the opinion of men, in order to try the faith of the disciples, lest their confession should appear to be founded on the common opinion. It goes on, And they answered, saying, Some say John the Baptist, some Elias, and others, One of the prophets.”