"Why could we not cast it out?"

And he said to them, “This kind cannot be driven out by anything but prayer.”  Mark 9:29

“You failed there, he said in effect to these disciples, because you did not have sufficient power.  You were using the power that you have, and you were very confident in it.  You did it with great assurance, you were masters of the occasion, you thought you were going to succeed at once, but you did not. . . . You will never be able to deal with ‘this kind’ unless you have applied to God for the power which he alone can give you.

"must become aware of your need, of your impotence, of your helplessness.  You must realize that you are confronted by something that is too deep for your methods to get rid of or to deal with, and you need something that can go down beneath that evil power and shatter it, and there is only one thing that can do that, and that is the power of God. . . .

"We must ask ourselves how we can succeed if we do not have this authority, this commission, this might and strength and power.  We must become utterly and absolutely convinced of our need.  We must cease to have so much confidence in ourselves, and in all our methods and organizations, and in all our slickness.  We have got to realize that we must be filled with God’s Spirit.

"And we must be equally certain that God can fill us with his Spirit.  We have got to realize that, however great ‘this kind’ is, the power of God is infinitely greater, that what we need is not more knowledge, more understanding, more apologetics, more reconciliation of philosophy and science and religion, and all modern techniques – no, we need a power that can enter into the souls of men and break them and smash them and humble them and then make them anew.  And that is the power of the living God.

"And we must be confident that God has this power as much today as he had one hundred years ago, and two hundred years ago, and so we must begin to seek the power and to pray for it.  We must begin to plead and yearn for it.  ‘This kind’ needs prayer.”

-- Martyn Lloyd-Jones, Revival (Wheaton, 1987), pages 18-19.
HT:  Ray Ortlund, Jr.