Matthew 16
A demand for a sign
The Pharisees and Sadducees came, and testing him, asked him to show them a sign from heaven. But he answered them, “When it is evening, you say, ‘It will be fair weather, for the sky is red.’ In the morning, ‘It will be foul weather today, for the sky is red and threatening.’ Hypocrites! You know how to discern the appearance of the sky, but you can’t discern the signs of the times! An evil and adulterous generation seeks after a sign, and there will be no sign given to it, except the sign of the prophet Jonah.” He left them and departed.
Pharisees and Sadducees test Jesus by asking for a sign from heaven. He replies that they can read the weather from the colour of the sky but not the signs of the times, and repeats that this generation will get no sign except the sign of Jonah. Then he leaves them.
What does this mean?
A 'sign from heaven' meant an unmistakable proof from God.
Historical context
Pharisees and Sadducees disagreed on much, including resurrection and the authority of tradition; Matthew shows them joining forces against Jesus. A red evening sky as a sign of fair weather is ancient weather lore found in many cultures.
Why does it matter?
The words about reading the sky are missing from some early manuscripts, though both the KJV and WEB include them. The repeated 'sign of Jonah' (12:39) points ahead to Jesus' death and resurrection.
Editorial notes, not scripture.