An evil and adulterous generation seeks for a sign, but no sign will be given to it except the sign of Jonah.” So he left them and departed. —Matthew 16:4 ESV
Earlier, in Matthew 12:39-40, we read that Jesus told his disciples the same thing:
But he answered them, “An evil and adulterous generation seeks for a sign, but no sign will be given to it except the sign of the prophet Jonah. For just as Jonah was three days and three nights in the belly of the great fish, so will the Son of Man be three days and three nights in the heart of the earth.
This repetition shows us that our Lord was in the habit of saying the same things over again. He did not content Himself with saying a thing once, and afterwards never repeating it. It is evident that it was His custom to bring forward certain truths again and again, and thus to impress them more deeply on the minds of His disciples. He knew the weakness of our memories in spiritual things. He knew that what we hear twice, we remember better than what we hear once. He therefore brought out of His treasury old things as well as new.
Now what does all this teach us? It teaches us that we need not be so anxious to harmonize the narratives we read in the four Gospels, as many are disposed to be. It does not follow that the sayings of our Lord, which we find the same in Matthew and Luke, were always used at the same time, or that the events with which they are connected must necessarily be the same. Matthew may be describing one event in our Lord’s life. Luke may be describing another. And yet the words of our Lord, on both occasions, may have been precisely alike. To attempt to make out the two events to be one and the same, because of the sameness of the words used, has often led Bible students into great difficulties. It is far safer to hold the view here maintained, that at different times our Lord often used the same words.