This is "A Man and a Woman seated by a Virginal" painted in the Dutch tradition around 1665. The woman is seated at the keyboard of the virginal, handing her partner a musical score for the violin next to him. Notice how his bow is nowhere to be seen, and he's offering her a glass of wine instead.
Scenes like this were common in seventeenth-century Dutch painting and often referred to romantic love. But Metsu may also be drawing a parallel between the innocent scene before us and something more...unseemly. That wine glass being offered could be seen as a phallic symbol, but it's quite subtle.
Look at the background - that's another of Metsu's works, showing a rowdy celebration on Twelfth Night. He's linking our quiet moment with the potential for debauchery, made possible by alcohol. The Latin inscriptions on the virginal seem to be a wry commentary on this situation, warning against loss of virtue while also advocating Christian worship.
It's interesting that Metsu uses the same instrument and inscriptions in other paintings. He may have been using them as models or exploring different themes within his work. Regardless, "A Man and a Woman seated by a Virginal" is a nuanced exploration of love, innocence, and the potential for transgression.
A Man and a Woman seated by a Virginal hangs in The National Gallery on Trafalgar Square, London — free to enter. Point your phone at any artwork there and audioguide.london plays a free audio guide in six languages — no app download needed.