Yea, as Agastya slew the foe, My hand shall lay Márícha low Clad in thine arms thy bow in hand, To guard the Maithil lady stand, With watchful eye and thoughtful breast Keeping each word of my behest I go, and hunting through the brake This wondrous deer will kill or take.

In plain words: Rama says he will kill Maricha just as Agastya killed his foe. He tells Lakshman to stay armed and guard Sita carefully, following his orders, while he goes to hunt the deer.