text: The bonfires are lit in memory of the miraculous escape that young Prahlad accomplished when Demoness Holika , sister of Hiranyakashipu , carried him into the fire . Holika was burnt but Prahlad , a staunch devotee of god Vishnu , escaped without any injuries due to his unshakable devotion .
simplified: Thus Prahlad came out of the burning fire safely and Holika was burnt to death .