For John said unto him, It is not lawful for thee to have her. - Here is an instance of zeal, fidelity, and courage, highly worthy of imitation. Plainness, mildness, and modesty, are qualifications necessary to be observed when we reprove the great. The best service a subject can render his prince is to lay before him, in the plainest but most respectful manner, what the law of God requires of him, and what it forbids. How unutterable must the punishment of those be who are chaplains to princes, or great men, and who either flatter them in their vices, or wink at their sins!

For John said unto him,.... John having heard of this incestuous marriage, went to Herod, and reproved him to his face for it; and, as Luke says, "for all the evils he had done", Luke 3:19 for he was a very wicked man, and guilty of many flagitious crimes: John, in so doing, showed his zeal for holiness, his hatred of sin, his courage and faithfulness in reproving thus freely so great a man; and made it manifest, that he came in the spirit of Elijah: what he said to him was,
it is not lawful for thee to have her, being forbidden, Leviticus 18:16 for though by another law it was right to marry a brother's wife, after his decease, when he left no issue, yet this was not the case here; Philip was now living, and, had he been dead, such a marriage would have been unlawful, because there was issue; she had a daughter, who afterwards is said to dance before Herod; and besides, he himself had another wife, whom he put away; so that his sin was a very aggravated and complicated one: lying with a brother's wife, was one of those sins which, according to the Jewish (h) canons, deserved cutting off, or death by the hand of God. Josephus (i) gives another reason of the imprisonment and death of John, that Herod feared that the people of the Jews, through his means, would be moved to sedition, and revolt from his government; which might be what Herodias suggested to him, or what he gave out himself, to cover the true cause of his proceedings: but the true reason is, what is here given, and is to be confirmed by the testimony of Jewish writers. One of their chronologers (k) delivers the account in these express words:
"Herod Antipater was a very wicked and pernicious man, many of the wise men of Israel he slew with the sword; and he took to wife, his brother Philip's wife, whilst he was living; and because John the high priest (for so through mistake they call him) "reproved him for this"; (see Luke 3:19) he slew him with the sword, with many of the wise men of Israel.''
And, says their historian (l),
"also he, Herod, slew John, because he said unto him, it is forbidden thee to take the wife of Philip, and he slew him; this is that John that practised baptism.''
(h) Misn. Ceritot, c. 1. sect. 1. (i) Antiqu. lsss. 18. c. 6. (k) Ganz. Tzemach David, par. 1. fol. 25. 2. (l) Joseph. Gorionides, 1. 5. c. 45.

It is not lawful for thee to have her. The marriage was unlawful for these three reasons: (1) The former husband of Herodias (Philip) was still living. (2) The former wife of Antipas was still living. (3) Besides, the Jewish law did not permit a man to marry his niece.

It is not lawful for thee to have her - It was not lawful indeed for either of them to have her. For her father Aristobulus was their own brother. John's words were rough, like his raiment. He would not break the force of truth by using soft words, even to a king.