What sign doest thou? This wickedness abundantly proves how truly it is said elsewhere, This wicked generation seeketh a sign, (Matthew 12:39.) They had been at first drawn to Christ by the admiration of his miracles or signs, and afterwards, through amazement at a new sign, they acknowledged Christ to be the Messiah, and, with that conviction, wished to make him a king; but now they demand a sign from him, as if he were a man unknown to them. Whence came such sudden forgetfulness, but because they are ungrateful to God, and, through their own malice, are blind to his power, which is before their eyes? Nor can it be doubted that they treat disdainfully all the miracles which they had already beheld, because Christ does not comply with their wishes, and because they do not find him to be what they imagined him to be. If he had given them expectation of earthly happiness, he would have been highly applauded by them; they would undoubtedly have hailed him as a Prophet, and the Messiah, and the Son of God; but now, because he blames them for being too much addicted to the flesh, they think that they ought not to listen to him any more. And in the present day, how many are there who resemble them! At first, because they promise to themselves that Christ will flatter their vices, they eagerly embrace the gospel, and call for no proof of it; but when they are called to deny the flesh and to bear the cross, then do they begin to renounce Christ and ask whence the gospel came. In short, as soon as Christ does not grant their prayers, he is no longer their Master.

What sign showest thou? - On the word sign, compare the notes at Isaiah 7:14. What miracle dost thou work to prove that thou art the Messiah? They had just seen the miracle of the loaves in the desert, which was sufficient to show that he was the Messiah, and it would seem from the preceding narrative that those who crossed the lake to see him supposed that he was the Christ. It seems wonderful that they should so soon ask for further evidence that he was sent from God; but it is not improbable that this question was put by other Jews, rulers of the synagogue, who happened to be present, and who had not witnessed his miracles. Those men were continually asking for signs and proofs that he was the Messiah. See Matthew 12:38-39; Mark 8:11; Luke 11:29. As Jesus claimed the right of teaching them, and as it was manifest that he would teach them differently from what they supposed Moses to teach, it was natural to ask him by what authority he claimed the right to be heard.

What sign - Τι σημειον, What miracle; so the word is evidently used, John 2:11, John 2:23, and in many other places.
That we may see, and believe thee - That, having seen the miracle, we may believe thee to be the promised Messiah. They had already seen the miracle of the five loaves, and did not believe; and it was impossible for them to see any thing more descriptive of unlimited power and goodness. Even miracles themselves are lost on persons whose hearts are fixed on the perishing things of the world, and whose minds are filled with prejudice against the truth.

(6) They said therefore unto him, What sign shewest thou then, that we may see, and believe thee? what dost thou work?
(6) The spiritual virtue of Christ is condemned by those that desire earthly miracles.

They said therefore unto him,.... Seeing he proposed believing in him as the grand work of God to be done, and what is most acceptable in his sight:
what sign showest thou then, that we may see and believe thee? The people of the Jews were always requiring signs and wonders, and when they had one and another shown them, they still sought for more, and were never satisfied; see Matthew 12:39. These men had lately seen various signs and miracles of Christ, as healing the sick, and feeding live thousand of them, and more, with five loaves, and two fishes; and though, for the time present, these had some influence upon them, and they were ready to believe he was that prophet; yet now, at least some of them, begin to retract, and signify, that unless some other, and greater signs were shown, they should not believe in him as the Messiah:
what dost thou work? more than others, or Moses. They seem to make light of the miracle of the loaves, or at least require some greater sign and miracle, to engage their belief in him as the Messiah; and as they were lovers of their bellies, and expected dainties in the times of the Messiah, they seem to move for, and desire miracles of that kind to be wrought; and which sense the following words confirm.

What sign showest thou, &c.--But how could they ask "a sign," when many of them scarce a day before had witnessed such a "sign" as had never till then been vouchsafed to men; when after witnessing it, they could hardly be restrained from making Him a king; when they followed Him from the one side of the lake to the other; and when, in the opening words of this very discourse, He had chided them for seeking Him, "not because they saw the signs," but for the loaves? The truth seems to be that they were confounded by the novel claims which our Lord had just advanced. In proposing to make Him a king, it was for far other purposes than dispensing to the world the bread of an everlasting life; and when He seemed to raise His claims even higher still, by representing it as the grand "work of God," that they should believe on Himself as His Sent One, they saw very clearly that He was making a demand upon them beyond anything they were prepared to accord to Him, and beyond all that man had ever before made. Hence their question, "What dost Thou work?"

What sign shewest thou then, that we may see, and believe thee? He had pointed to himself as the object of faith, making his claim, such as had never been made by mortal man. He had spoken of his seal, or sign. They ask now for a sign.

What sign dost thou? - Amazing, after what they had just seen!