Matthew 14:3

For Herod had laid hold on John, and bound him, and put him in prison for the sake of Herodias, his brother Philip's wife.

The Jews fiercely resented Herod's incestuous marriage with Herodias for three reasons: First, he was already married; second, she was his niece; and third, she was his brother's wife. The Jewish law expressly forbade a man's marrying his brother's wife, even after the brother's death, much less while he was still alive; the one exception being that when a man died without an heir, his brother was commanded to marry the deceased's widow and produce an heir to his estate (Leviticus 18:16; Deuteronomy 25:5-10).

Herod's imprisonment of John was due to the hatred of Herodias and shows what an evil influence can sometimes be exerted by an unprincipled woman in high place. Had it not been for the designs of the cruel, heartless, and immoral Herodias, John the Baptist might well have lived to see the Christ after his resurrection.