Expositor's Bible Commentary Commentary Mark 6:20

"for Herod feared John, knowing that he was a righteous and holy man, and kept him safe. And when he heard him, he was much perplexed; and he heard him gladly." — Mark 6:20 (ASV)

Herodias was infuriated by John and wanted to kill him. She was thwarted in her design because Herod protected John (motivated by fear and a recognition of John’s righteous and holy character).