The day described by Mark was "an opportune day" in that it suited Herodias' purposes. All of the very important people of Galilee were present for this birthday feast, and she would use these circumstances to her advantage.
Let it be understood that there is nothing inherently wrong with celebrating one's birthday, as long as it is done in a proper manner. However, the events of this feast were filled with lasciviousness and strong drink. The language used may indicate that other women had come in prior to Herodias' daughter, Salome, and had danced for the men. The text doesn't give us the details of her dancing, but, due to the reaction she gets, one may certainly conclude that she moved voluptuously and with the intent to arouse the lust of these men. One might rightly wonder why any woman would degrade herself before men in this manner, especially before her stepfather!
Herod was so pleased with her display that he swore to her - "Whatever you ask me, I will give you, up to half my kingdom" (Mark 6:23). Certainly these are the words of a man under the influence of intoxicants! Who, in their right mind, would promise under oath to give so much for so little? Herod was excited and flattered by this young woman and was willing to give away half of his kingdom for the sight of her immoral dance. His foolishness in making such a promise is easily apparent to us today, but how many in our day give away their souls for this and other sins? As foolish as Herod was, those who would forfeit everlasting life for the works of the flesh are even more senseless (cf. Matt. 16:26; Gal. 5:19-21). There are many Esaus today who are willing to sell their "birthright" for a "meal of stew" (Gen. 25:29ff).
Mark 6:24 shows the loyalty of Salome to her mother. She asks Herodias' counsel on this important decision. Of course, she was foolish to waste such an opportunity as this to satisfy the murderous revenge of her mother. She chose a bleeding head, severed from a body, over the wealth and honor of half the kingdom!
After hearing her request, "the king was exceedingly sorry; yet, because of the oaths and because of those who sat with him, he did not want to refuse her" (Mark 6:26). Herod is faced with a dilemma here: (1) If he grants her request, then he will be causing a just and holy man to be murdered; he knows that the common people will not favor him for this since they consider John to be a prophet, but (2) If he doesn't grant her request, then he will be breaking his oath and also looking foolish before all of these men of significance. He evidently came to the conclusion that his honor and respect were more precious than John's life. Had Herod not been in the presence of such evil men, perhaps he would not have granted this request.
Herod had the authority to have John beheaded without any trial of justice. His order was immediately carried out, and Herodias got what she wanted. John was no longer a threat to her "marriage." Her most dangerous "enemy" had been silenced, but murdering John did not alter the truth--she was still living in sin and had only compounded her guilt! When one fights against God's messengers, he fights against God Himself. Herodias believed she won this battle, but the Lord always wins the war!