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, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you. Matthew 17:20
The nine disciples were yet pondering upon the bitter fact of their own failure; and when Jesus was once more alone with them, they questioned, "Why could not we cast him out?" Jesus answered them, "Because of your unbelief: for verily I say unto you, If you 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." Their unbelief, that shut them out from deeper sympathy with Christ, and the carelessness with which they regarded the sacred work committed to them, had caused their failure in the conflict with the powers of darkness.
In order to succeed in such a conflict they must come to the work in a different spirit. Their faith must be strengthened by fervent prayer, and fasting, and humiliation of heart. They must be emptied of self, and be filled with the Spirit and power of God. Earnest, persevering supplication to God in faith--faith that leads to entire dependence upon God, and unreserved consecration to His work--can alone avail to bring men the Holy Spirit's aid in the battle against principalities and powers, the rulers of the darkness of tis world, and wicked spirits in high places. (The Desire of Ages, 429-431)
Reflection: Do you have a "mountain" in your life today? Pray with faith, knowing that God will do exactly as He says he will do, and then act upon it.