The speaker addresses someone who stands apart from everyone else, and compares them to a single red rose on a grey, empty plain. That image carries most of the poem. The person is striking enough to catch every eye, but their "thorns cut too deep," so others have pushed them away, or they have chosen to stay alone. The poem says it was loneliness "you chose to keep," which suggests the isolation is partly their own doing.
What stands out is the speaker's response. Instead of backing away, they accept the hurt: "cut as deep as you can." The speaker seems to know this person is dangerous to be close to, yet still finds them worth seeing. The final line asks only for "a small scar" as a keepsake, which sounds tender and a little sad. The mood is bittersweet, mixing admiration, longing, and quiet resignation, as though the speaker expects to lose this person but wants something to remember them by.