Albert Barnes on Matthew 16:21-23

See also Mk 7:31-33, Lk 9:22. From that time forth. This was the first intimation that he gave that he was to die in this cruel manner. He had taken much 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 theft minds for the awful event which 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 apprehensions of the proper character of the Messiah.

Elders. The men of the great council, or sanhedrim. Mt 5:7.

Chief Priests and Scribes. Mt 3:7.

(w) "From that time" Lk 9:22, 18:31, 24:6,7, 1Cor 15:3,4