When Dasaratha's three queens drank the paayasam, the four Vedas were born as four children for Dasaratha Rama, Lakshmana, Bharatha and Satrughna. Rama represented Yajur Veda, which is the embodiment of Dharma. Lakshmana, who was always immersed in reciting the name of Rama and ever dedicated to his service, represents the Rig Veda. Bharatha, who loved always to sing the name of Rama and revelled in chanting the Divine name, represents the Sama Veda. Satrughna, who was ever devoted to serving the other three brothers and who had conquered the internal and external foes, represents the Atharvana Veda.

The four brothers thus represented the four Vedas. It is only when the Ramayana is studied for its esoteric significance, rather than from a superficial point of view, that the full meaning of the epic be clear to us
Manifestation of Pranava

The significance of the advent of the four brothers may also be realised from another point of view. The Pranava mantra "Aum" has been equated with the Supreme Brahman. In this three letterword "A" stands for Lakshmana, "U" stands for Bharatha and "M" stands for Satrughna.

The Omkara that emanates from the combination of these three sounds represents Sri.Rama

Hence the scriptures have declared that the Rama Principle symbolises the primordial Omkara. Moreover, Valmiki brought out the unique significance of Rama, Lakshmana and Sita as a manifestation of Omkara. Lakshmana, representing "A", stands to the right of Rama; Rama, representing "U" is in the middle; and Sita, representing "M", is to the left of Rama. Valmiki described the combination of the three as the embodiment of divinity.

OMKAR and RAMA represent same

Sources: Sri Sathya Sai Baba Discourses