“Nay, idly mourn not,” Ráma cried, “The warrior king has nobly died, Intrepid hero, firm through all, So fell he as the brave should fall; And ill beseems it chiefs like us To weep for these who perish thus. Be firm: thy causeless grief restrain, And pay the dues that yet remain.”

In plain words: Rama tells Vibhishana not to grieve, because Ravana died bravely in battle, the way a warrior should. He asks him to stay strong and carry out the duties that are left.