Theophylact of Ohrid — as excerpted in the Catena Aurea on Mark 8:27-33

“But after the Lord had accepted the confession of the disciples, who called Him the true God, He then reveals to them the mystery of the Cross. Wherefore it goes on, And he began to teach them that the Son of man must suffer many things, and be rejected of the elders and of the chief priests, and the scribes, and be killed, and after three days rise again; and he spake that saying openly, that is, concerning His future passion. But His disciples did not understand the order of the truth, neither could they comprehend His resurrection, but thought it better that He should not suffer.”