The Pharisees and the Sadducees agreed on almost nothing, yet here they walk up together and ask Jesus for a sign from heaven. Matthew tells us why: they came 1"to test him." That phrase gives the whole request away. Jesus had just fed four thousand people in front of witnesses, so the sign they say they lack had already been given, more than once. What they wanted was a reason to keep disbelieving with a clear conscience.
Jesus answers by pointing at the sky, which they already read like experts. Red at evening means fair weather, and red and threatening in the morning means a storm. Any farmer or fisherman on that lake knew it, and Jesus turns it into his verdict: 3"you cannot interpret the signs of the times." The same minds that can forecast rain from a color go blind as soon as the sign in front of them asks for submission instead of observation. Their problem was a refusal dressed up as a request for more evidence.
He adds, 4"no sign will be given to it except the sign of Jonah." Jonah preached to pagan Nineveh, and mercy followed, because outsiders repented at the word of a reluctant prophet with no miracle attached. Here is someone greater than Jonah offering mercy to God's own covenant people, and the story runs the other way. Earlier in Matthew, Jesus has already explained what this sign is, his own death and resurrection. The men asking for proof are standing inside the answer.
Then the scene moves to a boat, and the failure changes from hostile to merely human. The disciples forgot to pack bread. Jesus is thinking of something else, and warns them, 6"Watch and beware of the leaven of the Pharisees and Sadducees." Every one of them assumes he means their lunch. 7"We brought no bread." He answers with what sounds like weary affection: 8"O you of little faith, why are you discussing among yourselves the fact that you have no bread?" These men had twice carried baskets of bread from his hands to thousands of people and twice carried the leftovers back.
Matthew closes the scene by telling us what Jesus meant. They understood that he was warning them about 12"the teaching of the Pharisees and Sadducees." Leaven works quietly. A small amount spreads through the whole lump without anyone announcing it. The teaching he means is the habit of asking for more evidence before obeying, and the disciples are not immune to it. Their version is gentler. Anxiety about lunch pushes out the memory of two miracles, and the effect is the same, because in both cases what has already happened stops governing how they read what is happening now.
So ask yourself what proof you are still waiting for before you obey, when God has already given more than you have counted. And when a new need makes you anxious, recount what he has done, by name, before you ask for another sign.
Prayer
Father, we can read so many things accurately, our finances, our weather, our schedules, and still miss what you have plainly done in our own lives. Give us a memory that works as faith, one that recounts your past provision the moment a new need makes us anxious. Save us from asking for another sign when the ones you have given are still sitting uncounted behind us. In Jesus' name, amen.