For one whose words so sweetly flow The whole Rig-veda needs must know, And in his well-trained memory store The Yajush and the Sáman’s lore. He must have bent his faithful ear All grammar’s varied rules to hear.

In plain words: Rama says that anyone who speaks this beautifully must know the holy Vedas well, the Rig, Yajur and Sama Vedas, and must have studied grammar carefully.