Someone tells the speaker, politely and kindly, to stop writing sad poems and write about happiness instead. Instead of cheering up, the speaker feels even lower. The request seems to dismiss what they actually feel, and the polite refusal to "take anything away" from their writing offers little comfort.
So the speaker digs out an old mask of good cheer and puts it on. At first it works: looking in the mirror, they feel good and see themselves grinning from ear to ear. But the last lines turn the poem around. The reflection has empty sockets where the eyes should be.
The mood is quiet, uneasy and bleak. The poem suggests that forced happiness is only a surface. The smile can be put on easily, but the eyes, which usually show what a person really feels, are missing. The title, "Empty," fits: pretending to be happy leaves the speaker hollow, not healed.