John Chrysostom
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.
But it is to be known, that, as ofttimes the faith of him that draweth near to receive supplies the miraculous virtue, so ofttimes the power of those that work the miracle is sufficient even without the faith of those who sought to receive. (Acts 10:4.) Cornelius and his household, by their faith, attracted to them the grace of the Holy Spirit; but the dead man who was cast into the sepulchre of Elisha, was revived solely by virtue of the holy body. (2 Kings 13:21.) It happened that the disciples were then weak in faith, for indeed they were but in an imperfect condition before the cross; wherefore He here tells them, that faith is the mean of miracles, Verily I say unto you, if ye shall have faith as a grain of mustard-seed, ye shall say to this mountain, Remove hence, and it shall remove.