John Lightfoot on Matthew 12:39

[An evil and adulterous generation seeketh after a sign.] I. Their schools also confessed, that signs and miracles were not to be expected but by a fit generation.

"The elders being once assembled at Jericho, the Bath Kol went forth and said, There is one among you who is fit to have the Holy Ghost dwell upon him, but that [this] generation is not fit. They fix their eyes upon Hillel the Elder. The elders being assembled again in an upper room in Jabneh, Bath Kol came forth and said, There is one among you who is fit to have the Holy Spirit dwell upon him, but that the generation is not fit. They cast their eyes upon Samuel the Little."

II. That generation by which and in which the Lord of life was crucified lay, and that deservedly, under an ill report for their great wickedness above all other, from the beginning of the world until that day. Whence that of the prophet, "Who shall declare his generation?" Isaiah 53:2; that is, his generation (viz. that generation in which he should live) should proceed to that degree of impiety and wickedness, that it should surpass all expression and history. We have observed before, how the Talmudists themselves confess, that that generation in which the Messias should come should exceed all other ages in all kinds of amazing wickedness.

III. That nation and generation might be called adulterous literally; for what else, I beseech you, was their irreligious polygamy than continual adultery? And what else was their ordinary practice of divorcing their wives, no less irreligious, according to every man's foolish or naughty will?

[But the sign of Jonah the prophet.] Here and elsewhere, while he gives them the sign of Jonah, he does not barely speak of the miracle done upon him which was to be equalled in the Son of man, but girds them with a silent check; instructing them thus much, that the Gentiles were to be converted by him, after his return out of the bowels of the earth, as heathen Nineveh was converted, after Jonah was restored out of the belly of the whale. Than which doctrine scarce anything bit that nation more sharply.