27 And Jesus saith unto them, All ye shall be offended because of me this night: for it is written, I will smite the shepherd, and the sheep shall be scattered.
'For it is written'
Awake, O sword, against my shepherd, and against the man that is my fellow, saith the Lord of hosts: smite the shepherd, and the sheep shall be scattered: and I will turn mine hand upon the little ones. Zech 13: 7
"Stumbled." is the idea -- confounded -- perplexed. Their minds were fixed on him in his kingly capacity. Something was about to happen for which they were totally unprepared, though he had sought to prepare them.
Nazareth Revisited Ch 53
72 And the second time the cock crew. And Peter called to mind the word that Jesus said unto him, Before the cock crow twice, thou shalt deny me thrice. And when he thought thereon, he wept.
It may seem strange that Peter the impulsive, the weak, and (by the Lord's denial) the dishonoured, should have been afterwards chosen as the Spirit's mouthpiece on the Day of Pentecost, and employed in the specially honourable office of holder and user of the keys of the Kingdom of Heaven, in opening the doors thereof officially and finally for Jew and Gentile, first for the Jews on the Day of Pentecost, and afterwards for the Gentiles at the house of Cornelius.
...Peter, the humbled... He would always remember the shame of having publicly denied the Lord. He would always feel like Paul, after him, that he was not worthy to be called an apostle. He was therefore qualified to fill the highest station in the ministration of the Spirit without being lifted up, for which his undoubted affectionate loyalty fitted him on another side of his character.
Nazareth Revisited Ch 52