Open the right wing of this small triptych and the scene looks almost too ordinary to matter: a carpenter at his bench, tools scattered around him, sunlight through a shuttered window. Only on close looking does an odd detail draw the eye. Twice over, the carpenter is shown finishing a small wooden mousetrap.
The Metropolitan Museum's own reading of the panel identifies the carpenter as Joseph, and reads his mousetraps through a specific piece of theology going back to Augustine. In this account, humanity had been ensnared by the devil the way an animal is caught by bait, and God's answer was to become bait himself: the Incarnation, God taking on ordinary human flesh in a Nazareth household, was the trap set to catch the trapper. Christ's humanity is the visible bait; his divinity is the trap's working part, hidden until it is too late for whatever it has caught.
It is a strange way to picture the central claim of Christian theology, mundane carpentry tools standing in for a cosmic reversal, and that strangeness is close to the point. The painters of this triptych were not illustrating a creed recited aloud in church. They found the doctrine already sitting inside an ordinary carpenter's workshop, hidden in plain sight the way the Incarnation itself, in this reading, hides God inside an ordinary human life.