Albert Barnes Commentary Matthew 16:21

"From that time began Jesus to show unto his disciples, that he must go unto Jerusalem, and suffer many things of the elders and chief priests and scribes, and be killed, and the third day be raised up." — Matthew 16:21 (ASV)

From that time forth. This was the first indication that he gave that he was to die in this cruel manner. He had taken great pains to convince them that he was the Messiah; he saw by the confession of Peter that they were convinced; and he then began to prepare their minds for the awful event that was before him.

Had he declared this when he first called them, they would never have followed him. Their minds were not prepared for it. They expected a temporal, triumphant prince, as the Messiah. He first, therefore, convinced them that he was the Christ; and then, with great prudence, began to correct their understandings of the proper character of the Messiah.

Elders. The men of the great council, or sanhedrim. See notes on Matthew 5:7.

Chief Priests and Scribes. See notes on Matthew 3:7.