This question is about the poem "Felix Randal"
Answer:
To reinforce that Randal died and that only the worst of him was remembered.
Explanation:
The last lines of the poem show that even though Randal showed a small improvement, he was unable to survive the disease and ended up dying. Furthermore, these last lines reinforce that even though Randal tried to be a better person in his last days, only the worst of him was remembered, the rest being erased from everyone's memories.