Rishi Vishwamitra used to perform Yajna. Mareech, Subahu etc. had always interrupted in Yajna. Vishwamitra rishi thought to bring Shri Rama to save the yajna. Vishwamitra visited Ajodhya, took a dip in Saryu River and reached in the assembly of Raja Dashratha. Dashratha ji welcomed him and said, due to good deeds of his ancestors, such a revered rishi came to his place. Raja Dashratha asked what service he could do for him. Vishwamitra blessed him and said to Raja Dashratha that his yajna has been interrupted by the Rakshasa and asked to send Shri Rama to save it. Raja Dasratha was trembled.
Raja Dashratha said to the rishi that he has got the sons in the old age with his blessings. He has four sons but Shri Rama is most affectionate to him. He could not survive without him. Shri Rama is very innocent, obedient, loves his brothers and pay high respect to him. Raja Dashratha became emotional while praising Shri Rama. Raja Dashratha pleaded the rishi that he could take his entire kingdom instead of Shri Rama as he is his life.
Vashisht ji explained Raja Dashratha that as per astrology, this year is destined for wedding of Shri Rama and his brothers. Hence, there is no hindrance in sending him. Vashisht ji said that he believes Vishwamitra has come for their wedding. Raja Dashratha was much elated to hear about their wedding. Then Raja Dashratha was ready to send Shri Rama. Shri Laxmana insisted to come along with Shri Rama to escort him. Both came in assembly and saluted everybody. Raja Dashratha asked them to save yajna of Vishwamitra. They readied and went to Mata Kaushaliya for blessings. She gave blessings and asked to obey the directions of their father.
Shri Rama and Laxmana walked along with Vishwamitra. On the way, they elevated Tarka. Vishwamitra was having his hermitage near Janakpur (now in Nepal). Shri Rama and Shri Laxmana started surveillance of yajna. Vishwamitra was offering the oblations in the fire and staring Shri Rama & Shri Laxmana.
Rakshasa reached to interrupt yajna. Repeated vision of Shri Rama, nature of Mareech transformed. He thought that interruption of yajna performed by Vishwamitra should not be done. He pondered over his transformation and concluded that by seeing the Shri Rama & Shri Laxmana, such thoughts have arisen.
Before completion of yajna, invitation came from Janakpur for the Swaymvar (selection of bride-groom) of Sita. Vishwamitra moved to Janakpur along with Shri Rama and Shri Laxmana after completion of yajna. On the way, Vishwamitra advised Shri Rama to touch a rock which was Ahilea. Ahilea came alive. Ahilea saluted Shri Rama. Gautam rishi, husband of Ahilea came there. Gautam rishi blessed Shri Rama that he would marry to a virtuous girl.
Yajna, Swadhya, Tapas and Dhyana do chitshudhi (चितशुद्धि). Chitshudhi does vision of almighty.
Source: Shrimad Bhagwat Mahapuran