At first glance, this could be just another painting for a Christmas card, but I would guess you'll never find it there. It's just a little too odd for a general audience.
This is a scene of the Adoration of the Shepherds. A rather diverse group of humble folk have gathered around Mary and her newborn babe. A large man strides forward from the right carrying a lantern and leading a large ox, while the man standing on the other side seems lost in thought. An old man and woman crouch down to get a better view, and a younger boy sneaks a peek over Mary's shoulder.
They have come to witness the birth of a savior. Mary and Jesus are clearly the focal point of the painting. They are the brightest element — so bright, in fact, that the baby seems to be a light source himself, which is no surprise given the notion that Jesus is the Light who came into the world to pierce the darkness. He certainly seems to do that here.
But that visual cue becomes so common in the Baroque Period that it seems hackneyed now. What is truly unusual about this painting is the young man with a budding moustache who is looking straight out at the viewer. It's a little uncomfortable, honestly. And it doesn't really make sense until you realize that the figure to his left is not another shepherd, but an angel, bedecked in fine robes, who seems to be jostling his way to the front of the crowd. The young man seems to put his hand up to prevent getting thwacked by a wing and looks out at us as if to say, "Do you see what's happening here? This is a little crazy." Indeed. This is crazy.
One more thing: Only the boy in the foreground seems to be missing the moment as he fiddles with a candle. In fact, he is so preoccupied by this little light right in front of his face that he doesn't look up to see the True Light. Look up! This is it! He's here!