John Lightfoot on John 12:39

[Therefore they could not believe, &c.] They were not constrained in their infidelity, because Isaiah had said, "Their heart is waxen gross," &c.; but because those things were true which that prophet had foretold concerning them: which prophecy, if I understand them aright, they throw off from themselves, and pervert the sense of it altogether.

"R. Jochanan saith, Repentance is a great thing; for it rescinds the decree of judgment determined against man: as it is written, 'The heart of this people is made fat, their ears heavy, and their eyes are closed, lest they should see with their eyes, and hear with their ears, and understand with their heart: but they shall be converted and healed,'" For to that sense do they render these last words, diametrically contrary to the mind of the prophet.

They have a conceit that Isaiah was cut in two, either by the saw or the axe, by Manasseh the king, principally for this very vision and prophecy:

"It is a tradition. Simeon Ben Azzai saith, I found a book at Jerusalem......in which was written how Manasses slew Isaiah. Rabba saith he condemned and put him to death upon this occasion: he saith to him, Thy master Moses saith, 'No man can see God and live': but thou sayest, 'I have seen the Lord sitting upon a throne, high and lifted up.' Thy master Moses saith, 'Who is like our God in all things that we call upon him for?' Deuteronomy 4:7: but thou sayest, 'Seek ye the Lord while he may be found,' Isaiah 55:6. Moses thy master saith, 'The number of thy days I will fulfil,' Exodus 13:26: but thou sayest, 'I will add unto thy days fifteen years,' Isaiah 38:5. Isaiah answered and said, 'I know he will not hearken to me in any thing I can say to him: if I should say any thing to the reconciling of the Scriptures, I know he will deal contemptuously in it.' He said therefore, 'I will shut myself up in this cedar.' They brought the cedar, and sawed it asunder. And when the saw touched his mouth, he gave up the ghost. This happened to him because he said, 'I dwell in the midst of a people of unclean lips.'"

Manasseh slew Isaiah, and, as it should seem, the Gemarists do not dislike the fact, because he had accused Israel for the uncleanness of their lips. No touching upon Israel by any means!