A single flow'r he sent me, since we met. (1)
The poem's very first words make us think of loneliness: "a" and "single." The single flower foreshadows or anticipates the woman's own feelings of loneliness.
Deep-hearted, pure, with scented dew still wet—One perfect rose (3-4).
The speaker's description here contrasts with her frustration. She clearly likes something about the rose, or likes something enough to spend two lines talking about it.
I knew the language of the floweret; (5)
The rhyme on "floweret" and "amulet" is interesting. It emphasizes the connection between nature and spiritual or emotional belief (like love) at the level of sound.