Wondrous blindness of the Pharisees and Sadducees! They asked a sign from heaven, as though the things they now saw were not signs. John shews what sign it was they desired; for he relates, that after the feeding with the five loaves, the multitudes came to the Lord and said, “What sign doest thou, that we may see it and believe on thee? Our fathers did eat manna in the desert, as it is written, He gave them bread to eat from heaven.” [John 6:30-31]
Therefore when they say here, Shew us a sign from heaven, they mean, Cause that it rain manna for one or two days, that the whole people may eat, as was done for a long time in the desert. He looking into their thoughts as God, and knowing that even if a sign from heaven should be shewed them they would not believe, would not give them the sign for which they asked, as it follows, “But he answered and said unto them, When the evening is come, ye say, It will be fair weather; for the sky is red, &c.”
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).