This elegantly-dressed young woman is seated at an instrument called "the Virginals". She is looking at us, not off to the side, as in The Guitar Player; this painting seems to be a reversion to the balanced, tranquil, interior scenes of the 1660's. Indeed the pose seems quite like A Lady Writing but without the luminous intensity.
Just as earlier compositions in rectangles seem to preview Piet Mondrian, so here we see the impressionists in the painting of the picture frame and the abstract fronds in the painting of the dress. Perhaps there is a Jackson Pollock preview on the side of the virginal!
The most ambiguous and fascinating aspect of this painting is, however, the subject of the prominent painting on the wall, which is Dirck van Baburen's The Procuress, depicting the point-of-sale transaction where a prostitute is bought. Why should a painting of sin be next to this innocent-looking young woman playing music? A contrast is provided by the apparently similar Lady Standing at the Virginals, but there the picture on the wall is of Cupid, implying that the "virginal" girl will fall in love. Perhaps we are to see a contrast between sin and innocence, or perhaps Vermeer is simply playing a joke on his audience....
Vermeer painted his own Procuress, and also used the Baburen picture in his The Concert. It is presumed that the Baburen picture hung in Vermeer's house; it is mentioned in the inventory of his mother-in-law's house from 1641.