Verse 32. - And he spake the saying openly (παῥῤησία); literally, without reserve. This sudden announcement excited St. Peter. It was a new and startling communication. Peter took him, and began to rebuke him. The word προσλαβόμενος indicates that he "took hold of him," to lead him apart, as though to have the opportunity of warning him with the greater familiarity and secrecy. So say St. Chrysostom and others. Peter would not have his own confession of Christ thus evacuated, as it were; nor does he think it possible that the Son of God could be slain. So he takes him apart, lest he should seem to reprove him in the presence of the other disciples; and then he says (Matthew 16:22), "Mercy on thee, Lord (ἵλεώς σοι Κύριε): this shall never be unto thee."

8:27-33 These things are written, that we may believe that Jesus is the Christ, the Son of God. These miracles of our Lord assure us that he was not conquered, but a Conqueror. Now the disciples are convinced that Jesus is the Christ; they may bear to hear of his sufferings, of which Christ here begins to give them notice. He sees that amiss in what we say and do, of which we ourselves are not aware, and knows what manner of spirit we are of, when we ourselves do not. The wisdom of man is folly, when it pretends to limit the Divine counsels. Peter did not rightly understand the nature of Christ's kingdom.And he spake that saying openly,.... Concerning his sufferings, death, and resurrection from the dead. He not only spoke it before them all, but in plain words, without a figure; so that it might be, and was clearly understood by them; and he spake it as the word will also bear, not only very freely, but likewise boldly, with an undaunted courage, with intrepidity of mind; being not in the least discouraged, nor showing any concern or fear about what was to befall him:

and Peter took him, and began to rebuke him. Peter might more especially be concerned at this free and open account Christ gave of his sufferings and death, because he had just now acquainted him, that he should have the keys of the kingdom of heaven; by which he might understand some high post in the temporal kingdom of the Messiah he expected; and immediately to hear of his sufferings and death, damped his spirits, and destroyed his hopes, and threw him into such difficulties he was not able to remove; and therefore he takes Christ aside, and very warmly expostulates with him about what he had said, and chides him for it, and entreats him that he would not think, or talk of such like things: the words of Peter are recorded by Matthew; see Gill on Matthew 16:22.