Dasarata's four sons represent four Vedas
When one is influenced by gunas, he develops desires. The four sons of Dasaratha were the embodiments of his desires. Rama, Lakshmana, Bharatha and Satrughna symbolise the four Vedas Rig, Yajur, Sama and Atharvana. The Rig Veda figures in the Yajur and Sama Vedas to varifying extent. It is the embodiment of Dharma. Yajur-Veda embodies mantras (sacred formulae). Lakshmana was continually engaged in contemplating about Rama and immersing himself in the Rama mantra. Bharata was one who could not bear separation from Rama and who was ever dwelling on Rama's name and form. He was the embodiment of Sama Veda. Shatrughna was one who had mastered all the sciences and used his powers for protecting his brothers. He was skilled in the use of all kinds of weapons. Thus the four Vedas, taking the form
of the four brothers, were sporting in Dasaratha's palace.
Source: Discourse in the Prashaanthi Mandir on 7-4-1987.