Death
The central theme of this poem is death. The poet finds it difficult to accept that his sister has died and still suffers as he feels that his life is buried with her. As in any traditional elegy, there is an introspection over the nature or meaning of death. The poet says that the sister is at peace as she rests.
Suffering
The poet also struggles as he has to live on despite the death of his sister. He says, "I vex my heart alone", indicating the suffering he is going through because of the death of his sister. He has suffered so much that he feels like his life is buried under the earth with his sister.
Peace
Peace is equated with death in this poem. The poet says that now his sister rests and there is peace. By this, he means that there is a certain peace once one is released from the bounds of life. In death all there is is peace, while the living go on to suffer.
