If Thou canst Believe - This was an answer to the inquiry above. I can furnish a sufficiency of power, if thou canst but bring faith to receive it. Why are not our souls completely healed? Why is not every demon cast out? Why are not pride, self-will, love of the world, lust, anger, peevishness, with all the other bad tempers and dispositions which constitute the mind of Satan, entirely destroyed? Alas! it is because we do not believe; Jesus is able; more, Jesus is willing; but we are not willing to give up our idols; we give not credence to his word; therefore hath sin a being in us, and dominion over us.

If.

Mark 11:23 For truly I say to you, That whoever shall say to this mountain, Be you removed, and be you cast into the sea...

2 Chronicles 20:20 And they rose early in the morning, and went forth into the wilderness of Tekoa: and as they went forth, Jehoshaphat stood and said...

Matthew 17:20 And Jesus said to them, Because of your unbelief: for truly I say to you, If you have faith as a grain of mustard seed...

Matthew 21:21,22 Jesus answered and said to them, Truly I say to you, If you have faith, and doubt not...

Luke 17:6 And the Lord said, If you had faith as a grain of mustard seed, you might say to this sycamine tree, Be you plucked up by the root...

John 4:48-50 Then said Jesus to him, Except you see signs and wonders, you will not believe...

John 11:40 Jesus said to her, Said I not to you, that, if you would believe, you should see the glory of God?

Acts 14:9 The same heard Paul speak: who steadfastly beholding him, and perceiving that he had faith to be healed,

Hebrews 11:6 But without faith it is impossible to please him: for he that comes to God must believe that he is...

Unbelieving Belief
'And straightway the father of the child cried out, and said with tears, Lord, I believe; help Thou mine unbelief.'--Mark ix. 24. We owe to Mark's Gospel the fullest account of the pathetic incident of the healing of the demoniac boy. He alone gives us this part of the conversation between our Lord and the afflicted child's father. The poor man had brought his child to the disciples, and found them unable to do anything with him. A torrent of appeal breaks from his lips as soon as the Lord gives …
Alexander Maclaren—Expositions of Holy Scripture

July the Ninth Scholars in Christ's School
"He taught His disciples." --MARK ix. 30-37. And my Lord will teach me. He will lead me into "the deep things" of God. There is only one school for this sort of learning, and an old saint called it the Academy of Love, and it meets in Gethsemane and Calvary, and the Lord Himself is the teacher, and there is room in the school for thee and me. But the disciples were not in the mood for learning. They were not ambitious for heavenly knowledge, but for carnal prizes, not for wisdom, but for place. …
John Henry Jowett—My Daily Meditation for the Circling Year

The Lenten Fast.
"This kind can come forth by nothing, but by prayer."--ST. MARK ix. 29. You remember the narrative from which I have taken this verse. Jesus, as we read, had just come down from the Mount of Transfiguration, and when He was come to the multitude, a certain man besought him saying, "Have mercy on my son, for he is lunatic and sore vexed, and I brought him to Thy disciples, but they could not cure him." Then Jesus rebuked the devil, and the child was cured from that hour. Thereupon His disciples …
John Percival—Sermons at Rugby