A man asked what looked like a simple question, and he expected a simple answer. Who is my neighbor? He wanted a line drawn on a map, a fence around his obligation, so he could know exactly whom he was required to love and feel at peace about everyone on the other side. He did not get a line. He got a road, a ditch, a beaten stranger, two respectable men of God who crossed to the far side and kept walking, and a foreigner from the wrong side of an old and bitter quarrel who stopped. And by the end the question had been turned inside out. Jesus never said who counts as a neighbor. He asked which of the three had proved to be one.

That quiet reversal may be the most radical thing ever said about mercy. It takes the whole machinery of us and them, the endless human habit of deciding who belongs inside the circle of our care, and dissolves it into a single act on a dangerous road. Neighbor, it turns out, is not a category you are born into. It is something you do.

This book walks the old story line by line, from the descent to Jericho to the two coins left with the innkeeper, and finds in it something sharper than a lesson about being nice. It is written by someone who once kept a house with an open door, where the hungry came in without being asked their religion or their papers, and who learned firsthand that living this parable can cost you everything and still leave you glad. It is honest about the ones who pass by, including the respectable and the devout. But it does not curse them. Like the Samaritan, it kneels instead.

Above all it is a book about joy, because mercy, rightly understood, is not a burden carried against the grain. The Samaritan is the lightest figure on that road, the only one not imprisoned by the accounting that told everyone else to keep walking. Written for anyone who has stood on the far side and wondered why, and for anyone ready to cross.