Theophylact of Ohrid — as excerpted in the Catena Aurea on Mark 10:32-34

“He did this to confirm the hearts of the disciples, that from hearing these things beforehand, they might the better bear them afterwards, and might not be alarmed at their suddenness, and also in order to shew them that He suffered voluntarily; for he who foreknows a danger, and flies not, though flight is in his power, evidently of his own will gives himself up to suffering. But He takes His disciples apart, because it was fitting that He should reveal the mystery of His Passion to those who were more closely connected with Him.”