It's almost a commonplace for us Franciscans to brag about how St. Francis invented the Nativity scene, or at least the live version.
But it's easy to forget about motives. He didn't do it to elicit sweet or pastoral feelings.
Francis' first biographer, Brother Thomas of Celano, quotes him:
I wish to enact the memory of the babe who was born in Bethlehem: to see as much as is possible with my own bodily eyes the discomfort of his infant needs, how he lay in a manger, and how, with an ox and an ass standing by, he rested on hay.
As always, Francis works in the tangible and concrete. He desires to see with his bodily eyes what he already sees with his heart: the poverty of Christ, the poor and humble Lord of the manger and of the Cross.
(The translation from Celano's Life is from the version included in the first volume of this series, which I recommend to all.)