Jamieson, Fausset and Brown on Judges 16:5

5. the lords of the Philistines--The five rulers deemed no means beneath their dignity to overcome this national enemy.

Entice him, and see wherein his great strength lieth--They probably imagined that he carried some amulet about his person, or was in the possession of some important secret by which he had acquired such herculean strength; and they bribed Delilah, doubtless by a large reward, to discover it for them. She undertook the service and made several attempts, plying all her arts of persuasion or blandishment in his soft and communicative moods, to extract his secret.