In plain words
When Sumitrā followed Vasiṣṭha's advice and laid Lakṣmaṇa beside Rāma and Śatrughna beside Bharata, the two stopped crying and began to gurgle with joy.
What is the inner meaning of this? Kausalyā had given Sumitrā half of her pāyasa, had she not! The one born of that half was Lakṣmaṇa. Since he was a part of Rāma, he went on following Rāma. In the same way, the one born of the pāyasa Kaikeyī gave was Śatrughna. Since he was a part of Bharata, he went on following Bharata. Bharata was born after Rāma. So Bharata was the second. Lakṣmaṇa was the third. But though he was the third, being a part of Rāma he joined himself to Rāma alone. In the same way, Śatrughna was always at Bharata's side. Rāma, Lakṣmaṇa, Bharata and Śatrughna, all four, grew up in close love for one another. Sumitrā was full of joy, thinking that when Rāma became king, Lakṣmaṇa would be his minister and serve him, and Śatrughna too would serve Bharata.
The ideal of Lakṣmaṇa
The kite that had snatched away Sumitrā's bowl of pāyasa let it fall on a hill, where Añjanādevī found it. Because she ate that pāyasa, a son was born to her. He was Hanumān. He met Rāma and Lakṣmaṇa while they were searching for Sītā in the forest. A close bond grew between them. When Hanumān took Rāma and Lakṣmaṇa to Sugrīva, Sugrīva brought out a bundle of jewels the monkeys had found in the forest and showed it to Rāma. It was the bundle of jewels Sītā had dropped while she was being carried off by Rāvaṇa. Husbands of today would make a list of all the jewels their wife has. But Rāma made no such list. “Lakṣmaṇa! Are these jewels your sister-in-law's? Look,” he said. Lakṣmaṇa looked at the jewels: “Brother! I do not know whose these jewels are, but the anklets I know are Mother Sītā's.