“sign of Jonah the prophet.” Here in Matthew 12:39-40, the “sign” of Jonah was that he was dead in the fish for three days and three nights, just like Jesus would be dead for three days and nights in the grave. This verse shows us how obscure a “sign” can be. We like to think that a “sign” is something that can clearly be understood. Today, sign makers spend many hours thinking about how to make their signs visible and easily understood so people know what is coming in the future. A “deer crossing” sign, for example, shows an image of a deer crossing the road so people of any language still understand the sign. But God has some signs that are not clear at all. Jonah disobeyed God and as a result ended up dead in a large fish (or perhaps a whale) for three days and three nights. Who knew that Jonah was a ‘sign” of the Messiah? When we look for patterns of the Messiah in the Old Testament, we have to be prepared to look prayerfully and patiently and use the New Testament to help identify and confirm them. They may not be clear.
Jesus also talked about the sign of Jonah in Luke 11:29-30. However, the “sign” of Jonah in Luke is different than the sign of Jonah in Matthew. In Luke, Jesus was teaching at a totally different time and place to a different audience. Here in Matthew, Jesus was in Capernaum, his hometown, and he was speaking to the Pharisees and experts in the Law, and he was answering their question about a sign that would show his authority to say the things he was saying. In contrast, in Luke, the evidence is that Jesus was in Perea, east of the Jordan River, and Jesus was teaching the multitudes, whom he was encouraging to repent and live a godly life (Luke 11:32). In Luke, Jesus pointed out that the unbelieving Ninevites repented when they heard Jonah, and since someone greater than Jonah was among them, they should repent.
In Luke, the Bible says that Jonah was a “sign” to the people of Nineveh, but they did not know anything about Jonah being dead in a fish (and they likely would not have believed it if he had told them). Nineveh was over 400 miles (650 km) from the Mediterranean Sea where Jonah had been swallowed by the great fish, and it likely took Jonah 3 months or so to reach Nineveh after the fish vomited Jonah out on the Phoenician shore. The “sign” of Jonah to the Ninevites was that a prophet of God came alone and unarmed into the capital city of an enemy country and boldly proclaimed the truth to them—that they would be destroyed if they did not repent—at the possible cost of his life. In fact, is it likely that Jonah’s life was spared only because the people of Nineveh believed him. Like Jonah, Jesus came and boldly preached the Gospel, but the Jews killed him.