ISB ~ Matthew 14 v4

It is not lawful:John publicly denounced the union of Herod Antipas and his mistress, Herodias. While the NT gives little background, extrabiblical history details how Antipas desired Herodias while she was married to his half-brother Herod Philip. Antipas and Herodias then abandoned their respective spouses in order to be united. The Mosaic Law, however, forbids the union of a man with his brother’s wife while the brother is still living (Lev 18:16; 20:21). Since Philip was yet living, John the Baptist spoke out against the union of Herod Antipas and Herodias and publicly disgraced them (Mk 6:19).