Diana is beautiful, intelligent and kind.
So many qualities.
Still, she feels weak sometimes.
When this happens, she undresses and looks into the mirror.
The painting acts as a container of what she felt one day. The painting is the mirror, somehow.
So she abandons herself to our eyes, which are greedy and useless.
She realizes that, and overcome her weakness.
We are nothing but greedy people.
She is nothing but beautiful, intelligent and kind.