
Augustine of Hippo
Catena Aurea · Matthäusevangelium 17
Then came the disciples to Jesus apart, and said, Why could not we cast him out? And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you. Howbeit this kind goeth not out but by prayer and fasting.
(ubi sup.) Otherwise; That the disciples in working their miracles should not be lifted up with pride, they are warned rather by the humbleness of their faith, as by a grain of mustard-seed, to take care that they remove all pride of earth, which is signified by the mountain in this place.