Jamieson, Fausset and Brown on Mark 6:26

26. And the king was exceeding sorry--With his feelings regarding John, and the truths which so told upon his conscience from that preacher's lips, and after so often and carefully saving him from his paramour's rage, it must have been very galling to find himself at length entrapped by his own rash folly.

yet for his oath's sake--See how men of no principle, but troublesome conscience, will stick at breaking a rash oath, while yielding to the commission of the worst crimes!

and for their sakes which sat with him--under the influence of that false shame, which could not brook being thought to be troubled with religious or moral scruples. To how many has this proved a fatal snare!

he would not reject her.