In plain words
‘I have undertaken a yajña. Send Rāma with me to guard that yajña from the rākṣasas’, asked Viśvāmitra. Hearing that, Daśaratha was deeply alarmed. “Great sage! Rāma is a little boy, tender and delicate. How can I send him to fight cruel rākṣasas!” he said. Viśvāmitra grew angry. “Daśaratha! Until now no one in the line of Ikṣvāku has gone back on his word. To break one's word is a great sin. It leads to great danger,” he warned.
How must he fulfil Viśvāmitra's wish? Daśaratha fell to thinking. When he consulted Vasiṣṭha, the sage heartened him: “Great king! Everything happens only as God wills. Give it no second thought, and send Rāma with Viśvāmitra,” he advised. Then Daśaratha: “Rāma! Come here,” he called. Lakṣmaṇa too came there along with Rāma. Nobody had called Lakṣmaṇa. He came of his own accord with Rāma and sat down. No one wished to send back a hero who had come forward. ‘Very well, this too is God's will!’ thought King Daśaratha, and he sent both Rāma and Lakṣmaṇa with Viśvāmitra.
The three reached the bank of the river Sarayū. Viśvāmitra: “Rāma and Lakṣmaṇa! The water of this river is most holy. Perform the sandhyā here,” he said. Rāma and Lakṣmaṇa performed the sandhyā, closed their eyes and sat in dhyāna. At that moment a thought arose in Viśvāmitra. “Those who come to yajñas and yāgas, children or elders, have to go without sleep and food. How can these princes, who eat on time and sleep on time, give up sleep and food and guard the yāga?” he thought. Then he taught them two mantras called ‘Bala’ and ‘Atibala’. “Rāma and Lakṣmaṇa! By the power of these mantras, sleep, hunger and thirst will not trouble you in the least.