Albert Barnes Commentary Judges 15:6

"Then the Philistines said, Who hath done this? And they said, Samson, the son-in-law of the Timnite, because he hath taken his wife, and given her to his companion. And the Philistines came up, and burnt her and her father with fire." — Judges 15:6 (ASV)

burnt her and her father - Out of revenge on Samson’s nearest relations; or, as others think, as an act of justice in favor of Samson, and in hope of pacifying his anger. Burning was the punishment for adultery and kindred crimes among the Jews (Genesis 38:24; Leviticus 20:14; Leviticus 21:9). Samson’s wife brought upon herself the very punishment which she sought to escape by betraying her husband (Judges 14:15).