Albert Barnes on Matthew 26:31

Then saith Jesus unto them, etc. The occasion of his saying this was Peter's bold affirmation that that he was ready to die with him, Jn 13:37. Jesus had told them that he was going away; i.e., was about to die. Peter asked him whither he was going. Jesus replied, that he could not follow then, but should afterwards. Peter, not satisfied with that, said that he was ready to lay down his life for him. Jesus then distinctly informed them that all of them would leave him that night.

All ye shall be offended because of me. Mt 5:29. It means, here, you will all stumble at my being taken, abused, and set at naught; you will be ashamed to own me as a teacher, and to acknowledge yourselves as my disciples. Or, my being betrayed will prove a snare to you all, so that you shall be guilty of the sin of forsaking me, and by your conduct of denying me.

For it is written, etc. See Zech 13:7. This is affirmed here to have reference to the Saviour, and to be fulfilled in him.

I will smite. This is the language of God the Father. I will smite, means either that I will give him up to be smitten, (compare Ex 4:21, 8:16, etc.,), or that I will do it myself. Both of thrum things were done. God gave him up to the Jews and Romans, to be smitten for the sins of the world, (Rom 8:32;) and he himself left him to deep and awful sorrows, to bear "the burden of the world's atonement" alone. See Mk 15:34.

The shepherd. The Lord Jesus--the Shepherd of his people, Jn 10:11,14; comp. Isa 11:11. The sheep. This means here particularly the apostles. It also refers sometimes to all the followers of Jesus, the friends of God, Jn 10:16; Ps 100:3.

Shall be scattered abroad. This refers to their fleeing, and was fulfilled in that. See Mt 26:66.

(e) "is written" Zech 13:7