Francis, recalling a visit he had made years before to Bethlehem, resolved to create the manger he had seen there. The ideal spot was a cave in nearby Greccio. He would find a baby (we’re not sure if it was a live infant or the carved image of a baby), hay upon which to lay him, an ox and an ass to stand beside the manger. Word went out to the people of the town. At the appointed time they arrived carrying torches and candles.
One of the friars began celebrating Mass. Francis himself gave the sermon. His biographer, Thomas of Celano, recalls that Francis “stood before the manger overcome with love and filled with a wonderful happiness ” For Francis, the simple celebration was meant to recall the hardships Jesus suffered even as an infant, a savior who chose to become poor for our sake, a truly human Jesus.
HT American Catholic.org