We know that a key to the enemy's city was one of the most valuable prizes in a war and that lovers were forever looking for the 'key' to each other's heart.
In a number of the artist's paintings, a key has a clear symbolism of an erotic (or sexual) artefact: see Keys of Passion, Keys and Key to the Heart of a Loved One.
This small painting sets out to provide one of the links in the love symbolism of the 'key-lock' sequence - the artifact of visualizing a love affair.
There are famous images by Degas of women taking a bath and drying themselves afterwards and here is how he explained the secret of such compositions:
"Naked figures are usually depicted posing for the viewer. I, however, paint the ordinary modest women, who are busy taking the usual care of their bodies... It is like watching them through a key-hole."
In this painting the watcher, having previously been in the dark, turns into a certain link in the love chain and becomes an artefact.
In the present triad of key, lock and key-hole, every symbol acquires its own meaning in time and shape.