Mat 12:39 An evil and adulterous generation seeks after a sign; and there no sign shall be given to it but the sign of the prophet Jonas:

While it sounds like Christ is clearly condemning the people of his age, our basic assumption is that all of his words are addressed to all people of all time. In the original Greek, his characterization of those around him can be read more sympathically.

The burdened offspring of adultery wish for proof, but no proof will be given to them but the proof of the prophet Jonah.

"Evil" is ponêros, which primarily means "oppressed by toils."

"Adulterous" is moichalis, which is a noun meaning "adulteress." This word is not really used in classical Greek.

"Generation" is genea, which means "race," "family," "offspring," and "age."

"Seeks after" is epizêteô which means "to seek after," "to wish for," and "to demand."

"Sign" is sêmeion, which means a "mark," "sign," or "proof." The word in Greek is used specifically to means a sign from the gods and it that sense, it means "omen," "portent," and "constellations."