And the great burthen wellnigh broke The neck untrained to bear the yoke. The royal swan outspeeds the crow: The steed is swift, the mule is slow, Nor can my feeble feet be led O’er the rough ways where thine should tread.

In plain words: Bharat says the burden nearly broke him, like a young ox not used to the yoke. He compares himself to a crow or a mule next to Rama, who is like a swan or a fast horse, and says he cannot walk the hard road a king must walk.