This is "An Evening Service in a Church" painted by Pieter Neeffs the Elder in 1649. You'll notice it's a nocturnal church interior, but not just any ordinary scene - it's during Mass. The chapel itself is lit up, providing enough light to see beyond into the dark church.
Look at the detail of the altar and the priest in front of it. He's wearing a richly decorated gold chasuble. To his sides are two altar boys holding long tapers, which they'll use to light the candles on the altar. On the walls you can see people kneeling in contemplation, some reading from prayer books or Bibles.
The altarpiece behind the priest has a piece of fabric with a red cross covering it - not just for decoration, but also possibly as a reference to Veronica's veil. Above the frame are three sculptures - Mary Magdalene and two angels. On the right side of the picture, you'll see a man sitting on a step, observing from a distance - he might be a beggar who has found refuge in the church.
What's interesting is that this painting is actually a more elaborate version of another work done by Neeffs' studio, "View of a Chapel at Evening". The figures here were painted by Bonaventura Peeters. This one lets you see beyond the chapel into the dark church, and has some key differences from its predecessor - like the different altarpieces and the fabric covering the one in this painting.
An Evening Service in a Church 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.