Matthew 10:7-9.
“And as they departed, Jesus began to say unto the multitudes concerning John, What went ye out into the wilderness to see? A reed shaken with the wind? But what went ye out for to see? A man clothed in soft raiment; behold, they that wear soft clothing are in kings' houses. But what went ye out for to see? A prophet? yea, I say unto you, and more than a prophet.”
For the matter indeed of John's disciples had been ordered well, and they had gone away assured by the miracles which had just been performed; but there was need after that of remedy as regarded the people. For although they could not suspect anything of the kind of their own master, the common people might from the inquiry of John's disciples form many strange suspicions, not knowing the mind with which he sent his disciples. And it was natural for them to reason with themselves, and say, “He that bore such abundant witness, has he now changed his persuasion, and does he doubt whether this or another be He that should come? Can it be, that in dissension with Jesus he says this? That the prison has made him more timid? That his former words were spoken vainly, and at random?” It being then natural for them to suspect many such things, see how He corrects their weakness, and removes these their suspicions. For “as they departed, He began to say to the multitudes.” Why, “as they departed?” That He might not seem to be flattering the man.
And in correcting the people, He does not publish their suspicion, but adds only the solution of the thoughts that were mentally disturbing them: signifying that He knew the secrets of all men. For He says not, as unto the Jews, “Wherefore think ye evil?” Because if they had it in their minds, not of wickedness did they so reason, but of ignorance on the points that had been spoken of. Wherefore neither does He discourse unto them in the way of rebuke, but merely sets right their understanding, and defends John, and signifies that he is not fallen away from his former opinion, neither is he changed, not being at all a man easily swayed and fickle, but steadfast and sure, and far from being such as to betray the things committed unto him.
And in establishing this, He employs not at first his own sentence, but their former testimony, pointing out how they bare record of his firmness, not by their words only, but also by their deeds.
Wherefore He says, “What went ye out into the wilderness to see?” as though He had said, Wherefore did ye leave your cities, and your houses, and come together all of you into the wilderness? To see a pitiful and flexible kind of person? Nay, this were out of all reason, this is not what is indicated by that earnestness, and the concourse of all men unto the wilderness. So much people and so many cities would not have poured themselves out with so great zeal towards the wilderness and the river Jordan at that time, had ye not expected to see some great and marvellous one, one firmer than any rock. Yea, it was not “a reed” surely, that “ye went out to see shaken by the wind:” for the flexible and such as are lightly brought round, and now say one thing, now another, and stand firm in nothing, are most like that.
And see how He omits all wickedness, and mentions this, which then especially haunted them; and removes the suspicion of lightness.
“But what went ye out for to see? A man clothed in soft raiment? Behold, they that wear soft clothing are in kings' houses.”
Now His meaning is like this: He was not of himself a waverer; and this ye yourselves showed by your earnestness. Much less could any one say this, that he was indeed firm, but having made himself a slave to luxury, he afterwards became languid. For among men, some are such as they are of themselves, others become so; for instance, one man is passionate by nature, and another from having fallen into a long illness gets this infirmity. Again, some men are flexible and fickle by nature, while others become so by being slaves to luxury, and by living effeminately. “But John,” says He, “neither was such a character by nature, for neither was it a reed that you went out to see; nor by giving himself to luxury did he lose the advantage he possessed.” For that he did not make himself a slave to luxury, his garb shows, and the wilderness, and the prison. Since, had he been minded to wear soft raiment, he would not have lived in the wilderness, nor in the prison, but in the king's courts: it being in his power, merely by keeping silence, to have enjoyed honor without limit. For since Herod so reverenced him, even when he had rebuked him, and was in chains, much more would he have courted him, had he held his peace. You see, he had indeed given proof of his firmness and fortitude; and how could he justly incur suspicions of that kind?
Source: Homilies on the Gospel of St. Matthew (New Advent)