Whereupon he promised with an oath to give her whatsoever she would ask.

People's New Testament

14:7 He promised with an oath to give her whatever she would ask. Herod confirms his promise by an oath. It was a common custom to reward a dancer or actor, on a great occasion like this, who pleased, and to ask what they wished. Herod knew that Salome danced because she had a request to make.

Matthew Henry's Concise Commentary

14:1-12 The terror and reproach of conscience, which Herod, like other daring offenders, could not shake off, are proofs and warnings of a future judgment, and of future misery to them. But there may be the terror of convictions, where there is not the truth of conversion. When men pretend to favour the gospel, yet live in evil, we must not favour their self-delusion, but must deliver our consciences as John did. The world may call this rudeness and blind zeal. False professors, or timid Christians, may censure it as want of civility; but the most powerful enemies can go no further than the Lord sees good to permit. Herod feared that the putting of John to death might raise a rebellion among the people, which it did not; but he never feared it might stir up his own conscience against him, which it did. Men fear being hanged for what they do not fear being damned for. And times of carnal mirth and jollity are convenient times for carrying on bad designs against God's people. Herod would profusely reward a worthless dance, while imprisonment and death were the recompence of the man of God who sought the salvation of his soul. But there was real malice to John beneath his consent, or else Herod would have found ways to get clear of his promise. When the under shepherds are smitten, the sheep need not be scattered while they have the Great Shepherd to go to. And it is better to be drawn to Christ by want and loss, than not to come to him at all.