Albert Barnes Commentary John 12:34

"The multitude therefore answered him, We have heard out of the law that the Christ abideth for ever: and how sayest thou, The Son of man must be lifted up? who is this Son of man?" — John 12:34 (ASV)

We have heard out of the law. That is, out of the Old Testament; or rather, we have been taught this by those who have interpreted the law to us.

That Christ. That is, the Messiah.

Abideth for ever. He will remain for ever, or will live for ever. The doctrine of many of them certainly was that the Messiah would not die, and that he would reign as a prince for ever over the people. This opinion was founded on such passages of Scripture as these: Psalms 110:4, Thou art a priest for ever; Daniel 2:44; Daniel 8:13–14.

In the interpretation of these passages, they had overlooked such places as Isaiah 53:1-12. Nor did they understand how the fact that he would reign for ever could be reconciled with the idea of his death. To us, who understand that his reign does not refer to a temporal, an earthly kingdom, it is easy.

How do you say, etc. We have understood by the title "the Son of man" the same as the Messiah, and that he is to reign for ever. How can he be put to death?

Who is this Son of man? "The Son of man we understand to be the Messiah spoken of by Daniel, who is to reign for ever. To him, therefore, you cannot refer when you say that he must be lifted up, or must die. Who is it—what other Son of man is referred to but the Messiah?" Either ignorantly or willfully, they supposed he referred to someone else other than the Messiah.

For the phrase "out of the law," see Romans 5:18; Psalms 72:17–19.