Whereupon he promised with an oath
On account of her fine dancing, and being extremely pleased with it himself; and the more, that it gave such pleasure to the whole court: he first promised her,
to give her whatsoever she would ask;
and then repeating it, he confirmed it with an oath; adding, as Mark says, that he would give it her, even "to the half of his kingdom": a way of speaking used by princes, when they give full power to persons to ask what they will of them; and to express their great munificence and liberality; signifying, let it be ever so great, or cost what it will, though as much as half a kingdom comes to, it shall be granted; see ( Esther 5:3 Esther 5:6 ) . A very foolish promise, and a rash oath these, which were made upon such a consideration, as only a fine dance. If she, as Theophylact observes, had asked for his head, would he have given it her? And if he swore by his head, which was a common form of swearing with the Jews F21, she very appropriately, though unjustly, as Dr. Lightfoot observes, answers to him; as you have swore by your head, give me John Baptist's head.
F21 Misn. Sanhedrim, c. 3. sect 2. T. Bab. Beracot, fol. 3. 1. Derech Eretz, c. 6. fol. 18. 2.