Sita undergoes 'Agni Pariksha' (an ordeal of fire) by which she proves her chastity before she is accepted by Rama

Sita undergoes 'Agni Pariksha' (an ordeal of fire) by which she proves her chastity before she is accepted by Rama. Rama knew that Sita was perfect and Sita too knew that Rama does not have a single doubt on her. But they wanted the world to realize that Sita was pure despite she was in Ravana's custody. This is why Rama asked Sita to do the 'Agni Pariksha'..