And Jesus said unto them,
Because of your unbelief: for verily I say unto you, If you have faith as a grain of mustard seed, you shall say unto this mountain, Remove from here to yonder place; and it shall remove; and nothing shall be impossible unto you.
All Commentaries on Matthew 17:20 Go To Matthew 17
George Leo Haydock
AD 1849
See here the efficacy of prayer and fasting! What the apostles could not do, prayer accompanied with fasting can effect. How then can that be genuine religion, which makes fasting an object of ridicule? We see also here that the true Church in her exorcisms follows Scripture, when she uses besides the name of Jesus, many prayers and much fasting to drive out the devils, because these, as well as faith, are here required. (Bristow)