Why then dost thou baptize? By laying down those three degrees, they appear to form a very conclusive argument: if thou art not the Christ, nor Elijah, nor a prophet; for it does not belong to every man to institute the practice of baptism. The Messiah was to be one who possessed all authority. Of Elijah who was to come, they had formed this opinion, that he would commence the restoration both of the royal authority and of the Church. The prophets of God, they readily grant, have a right to discharge the office committed to them. They conclude, therefore, that for John to baptize is an unlawful novelty, since he has received from God no public station. But they are wrong in not acknowledging him to be that Elijah who is mentioned by Malachi 4:5; though he denies that he is that Elijah of whom they foolishly dreamed.

Why baptizest thou then - Baptism on receiving a proselyte from "paganism" was common before the time of John, but it was not customary to baptize a "Jew." John had changed the custom. He baptized "all," and they were desirous of knowing by what authority he made such a change in the religious customs of the nation. They presumed, from the fact that he introduced that change, that he claimed to be a prophet or the Christ. They supposed that no one would attempt it without "pretending," at least, authority from heaven. As he disclaimed the character of Christ and of the prophet Elijah, they asked whence he derived his authority. As he had just before applied to himself a prediction that they all considered as belonging to the fore runner of Christ, they "might" have understood "why" he did it; but they were blind, and manifested, as all sinners do, a remarkable slowness in understanding the plainest truths in religion.

Why baptizest thou then? - Baptism was a very common ceremony among the Jews, who never received a proselyte into the full enjoyment of a Jew's privileges, till he was both baptized and circumcised. But such baptisms were never performed except by an ordinance of the Sanhedrin, or in the presence of three magistrates: besides, they never baptized any Jew or Jewess, nor even those who were the children of their proselytes; for, as all these were considered as born in the covenant, they had no need of baptism, which was used only as an introductory rite. Now, as John had, in this respect, altered the common custom so very essentially, admitting to his baptism the Jews in general, the Sanhedrin took it for granted that no man had authority to make such changes, unless especially commissioned from on high; and that only the prophet, or Elijah, or the Messiah himself; could have authority to act as John did. See the observations at the conclusion of Mark.

And they asked him, and said unto him, (l) Why baptizest thou then, if thou be not that Christ, nor Elias, neither that prophet?
(l) By this we may prove that the Jews knew there should be some change in religion under the Messiah.

And they asked him, and said unto him,.... They put a question, by saying to him,
why baptizest thou then, if thou be not that Christ, nor Elias, neither that prophet? since he denied that he was the Messiah, or Elias that was to come before the Messiah, according to the expectation of the Jews, or that prophet, or a prophet, they demand by what authority he introduced a new rite and ordinance among them, which they had never been used to; for though there were divers washings or baptisms among them, enjoined by the law of Moses in certain cases, and others which obtained by tradition, as the immersion of themselves after they had been at market, and of cups, pots, brazen vessels, and tables, yet nothing of this kind that John administered: and as for the baptism of proselytes, it seems to be of a later date than this, and had no manner of likeness to it. The ordinance John administered was such, as they apprehended that no one ought to practise, unless he was the Messiah, or his forerunner, or some eminent prophet; they insist upon it therefore, that since he denied he was either of these, that he would show his credentials, and what commission he had from God to baptize; or they suggest he was liable to be called to an account by their sanhedrim, and be condemned as a false prophet, or an innovator in religious affairs. From hence it appears, that the Jews expected that baptism would be administered in the times of the Messiah, and his forerunner; but from whence they had this notion, it is not easy to say, whether from Zac 13:1 as Grotius, or from Ezekiel 36:25 as Lightfoot; nor do they speak contemptibly of it, but rather consider it as a very solemn affair, to be performed only by great personages: and this may teach modern ones to think and speak more respectfully of this ordinance than they do, who have given themselves great liberties, and have treated it with much contempt and virulence; calling it by the names of uncleanness, abomination, filthy water, and a devoting of persons to Satan (z): likewise, it is clear from hence, that they expected that this ordinance would be first administered by some person of very great note, either some very famous prophet, as Elias, whom they looked for before the coming of the Messiah, or else the Messiah himself, and not by a common teacher, or any ordinary person; wherefore this rite, as performed by John, could have no likeness with any thing that was in common use among them: besides, it was expressly done in the name of the Messiah, Acts 19:5 therefore they conclude he, or his forerunner, must be come; and that John must be one, or other of them, otherwise, why did he administer it? and it is also evident from hence, that no such practice had obtained before among them, or they would not have been alarmed at it, as they were; nor would they have troubled themselves to have sent after John, and inquire of him who he was, that should practise in this manner,
(z) Vet. Nizzachon, p. 56, 62, 64, 70, 74, 77, 148, 191, 193.

Why baptizest thou, if not, &c.--Thinking he disclaimed any special connection with Messiah's kingdom, they demand his right to gather disciples by baptism.

Why baptizest thou then? If he were Christ, or Elias, or "that prophet," they could understand why he should establish a new religious rite, but if none of these, why should he do so? Their perplexity shows that the baptismal rite was new to them. There is no proof that Jewish proselyte baptism of Gentile converts existed at this period, save the assertion of the Talmud, written two or three centuries after this. Josephus, who wrote in the time of the apostles, is silent about it.

They asked him, Why baptizest thou then? - Without any commission from the sanhedrim? And not only heathens (who were always baptized before they were admitted to circumcision) but Jews also?