
Gregory the Great
Catena Aurea · Matthäusevangelium 13
Another parable put he forth unto them, saying, The kingdom of heaven is like to a grain of mustard seed, which, a man took, and sowed in his field: Which indeed is the least of all seeds: but when it is grown, it is the greatest among herbs, and becometh a tree, so that the birds of the air come and lodge in the branches thereof.
(ubi sup.) The birds lodge in its branches, when holy souls that raise themselves aloft from thoughts of earth on the wings of the virtues, breathe again from the troubles of this life in their words and comfortings.