Here is a speaker who decides to be their own judge. Standing undressed in front of a mirror, they say that even if nobody else sees their beauty, they do. The opening line, "In my eyes, if not in anyone else's," admits that other people may disagree, but the speaker doesn't let that matter.
The feeling is confidence, and it feels earned rather than boastful. The speaker doesn't compare themselves to anyone. They simply look and approve. The image of "every stroke delicately placed" turns the body into a painting, as if each detail was made with care, and the final line, "I am a masterpiece," states the idea outright. Being unclad suggests honesty and comfort, with nothing hidden or dressed up.
The mood is calm, proud and quietly defiant. The poem's title, "The Beholder," points to the old saying that beauty is in the eye of the beholder, but here the speaker is both the artwork and the viewer.