After all the miracles Jesus has done, why do the Pharisees and Sadducees demand a sign (Matthew 16:1)? This is a test (πειράζω), which may be a positive test, giving a person a chance to prove themselves. If Jesus can show them a sign from heaven, then he will have proven his claims to be God’s special representative, maybe even prove he is the Messiah.
Matthew 16:1-12 looks back to the two miraculous feeding miracles in 14:13-21 and 15:29-39, but also anticipates Peter’s confession in 16:13-20 and the surprising revelation of what the Messiah’s mission is all about (16:21-28). Although he has not yet openly claimed to be the Messiah, he has done a series of powerful signs which ought to point to the fact he is the “one who is coming” (Matt 11:4-6). Instead of seeing these clear and obvious signs, the religious leaders of the day, the Pharisees (and now the Sadducees) question whether he is the Messiah, or whether he is in league with Beelzebul, the devil himself. The Pharisees and Sadducees now come to Jesus once again and demand to see a “sign from heaven” to prove his authority comes from God. The next time we meet the Pharisees they are testing Jesus on interpretation of divorce law (19:3) and they will seek to arrest Jesus when he arrives in Jerusalem (21:45).
That Pharisees and Sadducees join forces to test Jesus is remarkable since they rarely appear together in non-biblical documents. This would be the equivalent of Bernie Sanders and Donald Trump working together on some political issue (so, impossible). An additional problem is Matthew locating the Sadducees in Galilee. Mark 8:11 only has the Pharisees, scholars usually point out Sadducees were not active beyond Jerusalem. Matthew has added them at this point in the story to emphasize how serious the religious authorities were taking Jesus’s growing movement. However, Matthew 3:7 indicates both Pharisees and Sadducees went out to hear John’s teaching as his movement grew. Representatives of both groups went out to see if John was claiming to be the messiah or if there was any reason to worry about his influence over the people. (Again, imagine an issue so important that Bernie Sanders and Donald Trump would go on a “fact finding mission” because they were both troubled by that issue.)
Even when the disciples of John the Baptist came to Jesus to ask if he was “the one to come,” Jesus responded by pointing out the messianic signs which indicate he is the one anticipated by Isaiah 61 (Matt 11:1-24).
In the context of the feeding of the 5000 and 4000 in the wilderness, it is possible Matthew wants us to remember Israel testing God in the wilderness. In Exodus 17:2, for example, when the people quarreled (KJV, “they did chide with the Lord,” in the next few verses they “murmur”) about lack of water, Moses said “Why do you test the Lord?” (LXX τί πειράζετε κύριον;). Testing God is a major theme of the book of Numbers. Israel constantly tests God by their complaints and demands. Satan tested Jesus in Matthew 4:3, clearly an example of trying to trap Jesus in sin.
The demand is for “a sign from heaven,” something which will demonstrate the source of Jesus’s authority. This is an intensification of the demand by the Pharisees to do a sign (12:38, to which Jesus would only give the sign of Jonah). In Matthew 12:38, “we wish to see a sign” becomes a demand.
It is possible this means, “a sign from God” since Jews avoid saying the name of God (compare to Matthew’s kingdom of heaven vs. Mark’s Kingdom of God). Davies and Allison disagree, this is not a periphrasis. They suggest the Pharisees and Sadducees want Jesus to do a miracle that is unambiguously from God like a voice from heaven, for example (Davies and Allison, Matthew 2:579). All his miracles so far are earthly miracles, so a healing or exorcism could be done by God or the power of Satan.
The demand for a sign may be based on two contrasting stories in Isaiah. In Isaiah 7:11, the Lord tells King Ahaz he will protect him from his enemies and offers to do any sign Ahaz desires, “whether in the deepest depths or the highest heights.” In that case, Ahaz refuses to demand a sign but the Lord gives him the sign of Immanuel anyway. In Isaiah 38 Hezekiah falls ill, calls on the Lord, and is told he will survive and live for fifteen more years. The Lord offers him a sign in 38:7, a shadow cast by the sun will go back ten steps. Sunlight going backwards is a “sign from heaven.”
Later in Matthew 24:27, Jesus describes a sign from heaven: “For as the lightning comes from the east and shines as far as the west, so will be the coming of the Son of Man.” The “sign of the coming of the Son of Man” will be an unmistakable cosmic sign in the heavens. (Matthew 24:28 is also a sign in the heavens, “wherever the corpse is, the vultures will gather.”
Once again Matthew is presenting Jesus in the light of the grand stories of the Old Testament, Moses in the wilderness or even as a prophet like Isaiah. By demanding a sign from Jesus, the Pharisees are testing God.