Two literary devices that can be found in the poem are personification and simile. The Rose is personified throughout the whole poem and we know this because the Kipling capitalizes it making it a proper noun like a person. The Rose is spoken to and speaks. Also Dark, Time, Space, and Tide are personified.
The simile is found in the second stanza and reads,
"Then softly as a rain-mist on the sward
Came to the Rose the Answer of the Lord:"
This simile is making a comparison using the word "as" to compare how softly the answer from the Lord came to the Rose, it came as softly as rain mist on a sword.
The theme of the poem is about life and death, heaven and hell. This rose is dying after being blown from the bush and it has a conversation with God about how it fell and who heard it fall. She curses God for what has happened to her and he comes to her side. He asks her why she is so upset and what she heard when she fell and she says she heard a voice asking her why the flower fell, then she heard a voice telling her it was Allah's will that she lay dying. God answers her by saying not to cry out against things that are eternal like Dark, Tide, Time and Space. They cannot help that they will exist forever, but they do not live. He tells her that she dies because she must just like everything else that is living and the voice which asked can save itself from Hell because it sought understanding.