From Commentary on Luke (ca. 378)
Christ says, “If you had faith as big as a mustard seed, you would say to this tree, this mulberry tree: tear yourself away and throw yourself into the sea; and he would listen to you.” … What profit would there be for us for a tree, made to give fruit to the toilers who toil, is uprooted and thrown into the sea? Doubtless we believe it possible, by virtue of faith, that insensible nature obeys perceptible orders… In another book of the Gospels (Matt. 17:19), Christ speaks of a mountain – whose bare silhouette, deprived of fertile vineyards and olive trees, barren in harvests, conducive to the dens of animals, troubled by the incursions of wild beasts… This passage is therefore an exhortation to the faith; in the moral sense Christ teaches us that even what is most solid can be destroyed by faith. But from faith come charity, from charity hope, and they come back to one another as by a sacred circle.
St. Ambrose (ca. 334-397) became Archbishop of Milan at a time of bitter strife about Christological doctrine, and upheld orthodox teaching in a his widely circulated sermons and treatises. He is credited with introducing hymns to the Western Church, some composed by himself, and his greatest disciple was the even more influential St. Augustine. His commentary on St. Luke is based on a series of expository sermons he preached in his cathedral. His feast day is December 7.