The accounts of the death of John the Immerser are recorded in the following places: Matthew 14:1-12 and Mark 6:14-29.
First, I would like to answer a frequently asked question: why do I refer to John as “John the Immerser” instead of “John the Baptist” as he is called in most English translations. The reason is, the words “John the Immerser” more accurately represent the Greek phrase Ioannes ho Baptistes. In other words, the phrase indicates John was a man who immersed or submerged people.
There is not one specific reason why John was beheaded. Several factors contributed to John’s beheading.
(1) John was beheaded because he told a political monarch that he had no right to his brother’s wife! (Matthew 14:4) John’s choices were to ignore the facts even though Herod needed to know the truth, or tell Herod exactly what he needed to know. People often say, “Tell me the truth,” but when they are told the truth they resent it. John lost his life because he stood with God’s will. (Revelation 2:10)
(2) John was also beheaded because he offended Herodias, the unlawful wife of Herod! (Mark 6:19) She nursed a grudge against John. A scorned woman can be an instrument of death. No doubt Herodias had an emotional attachment with Herod, but John was obligated to tell the truth. He did and as a result he lost his life.
(3) John was beheaded because Herodias’ daughter danced for Herod’s guest and it pleased Herod. Herod promised with an oath to give her whatever she asked. (Matthew 14:6-7) She said, “Give me on a platter the head of John the Immerser.” Her request was granted, even though it distressed King Herod. John died in order to live forever with God!