Matthew 14:4

Then his narrative proceeds thus: "For Herod had laid hold on John, and bound him, and put him in prison, for Herodias' sake, his brother Philip's wife. For John said unto him, It is not lawful for thee to have her. And when he would have put him to death, he feared the people, because they counted him as a prophet." And wherefore doth he not address his discourse at all to her, but to the man? Because it depended more on him. But see how inoffensive he makes his accusation, as relating a history rather than bringing a charge.

(ord.) And perhaps he observed the Jewish Law, according to which John forbade him this adultery.

The old history tells us, that Philip the son of Herod the greater, the brother of this Herod, had taken to wife Herodias daughter of Aretas, king of the Arabs; and that he, the father-in-law, having afterwards cause of quarrel with his son-in-law, took away his daughter, and to grieve her husband gave her in marriage to his enemy Herod. John the Baptist therefore, who came in the spirit and power of Elias, with the same authority that he had exerted over Ahab and Jezebel, rebuked Herod and Herodias, because that they had entered into unlawful wedlock; it being unlawful while the own brother yet lives to take his wife. He preferred to endanger himself with the King, than to be forgetful of the commandments of God in commending himself to him.

(De Cons. Ev. ii. 44.) Luke does not give this in the same order, but where he is speaking of the Lord's baptism, so that he took beforehand an event which happened long afterwards. For after that saying of John's concerning the Lord, that His fan is in His hand, he straightway adds this, which, as we may gather from John's Gospel, did not follow immediately. For he relates that after Jesus was baptized, He went into Galilee, and thence returned into Judæa, and baptized there near to the Jordan before John was cast into prison. But neither Matthew nor Mark have placed John's imprisonment in that order in which it appears from their own writings that it took place; for they also say that when John was delivered up, the Lord went into Galilee, and after many things there done, then by occasion of the fame of Christ reaching Herod they relate what took place in the imprisonment and beheading of John. The cause for which he had been cast into prison he shows when he says, On account of Herodias his brother's wife. For John had said unto him, It is not lawful for thee to have her.