John 12:34 - Matthew Poole's English Annotations on the Holy Bible

Here again the law is taken in a larger sense than in some places, where it is only significant of the books of Moses, in opposition to the prophets and other holy writings, as we had it before, 1 Thessalonians 10:34; for the places of Scripture which the people seem to refer to, seem to be Psalms 110:4, where Christ is called a priest for ever; or else Daniel 7:14, where the kingdom of the Messiah is said to be an everlasting dominion, which should not pass away, a kingdom that should not be destroyed: so also, Daniel 2:44 Micah 4:7. These old prophecies of the Messiah the people could not reconcile to what our Saviour here told them of his death; the reason was, their not understanding the true notion of the Messiah, and of his kingdom, which they fancied not to be a spiritual and eternal kingdom, but a temporal kingdom here on earth. This made them ask, how, (that is, with what consistency to those prophecies), if he indeed were the Messias, he said, The Son of man should die; for that they understood by the term lifted up, which maketh it very plain, that it was a phrase they used to express that kind of death by. They ask who he meant by the Son of man.