Ellicott's Commentary for English Readers - Matthew 12:40
(40) As Jonas was three days and three nights.—To understand the words rightly, we have to remember the prominence which our Lord gives to the history of Jonah, and to the repentance of the men of Nineveh, in this and in the parallel passage of Luke 11:29, and in answer to another demand for a sign in Matthew 16:4. In the other passages “the sign of the prophet Jonas” appears with a vague mysteriousness, unexplained. Not a few critics have accordingly inferred from this difference that the... read more
Ellicott's Commentary for English Readers - Matthew 12:39
(39) An evil and adulterous generation.—The true relation between Israel and Jehovah had been represented by the prophets as that of the wife to her husband (Jeremiah 3:0; Ezekiel 16:23; Hosea 1:2). The adulterous generation was therefore one that was unfaithful to its Lord—demanding a sign, instead of finding sufficient proofs of faithfulness and love in what He had already done.There shall no sign be given to it.—The words seem at first to place our Lord’s miracles of healing outside the... read more