Counting The Cost, By C.S. Lewis:

"The terrible thing, the almost impossible thing, is to hand over your whole self--all your wishes and precautions--to Christ.
"Christ says 'Give me All. I don't want so much of your time and so much of your money and so much of your work: I want You. I have not come to torment your natural self, but to kill it. No half measures are any good. I don't want to cut off a branch here and a branch there, I want to have the whole tree down. I don't want to drill the tooth, or crown it, or stop it, but to have it out. Hand over the whole natural self, all the desires which you think innocent as well as the ones you think wicked--the whole outfit. I will give you a new self instead. In fact, I will give you Myself: My own will shall become yours.'...
"When I was a child I often had toothache, and I knew that if I went to my mother she would give me something which would deaden the pain for that night and let me get to sleep. But I did not go to my mother--at least not till the pain became very bad. And the reason I did not go was this. I did not doubt she would give me the aspirin; but I knew she would also do something else. I could not get what I wanted out of her without getting something more, which I did not want. I wanted immediate relief from pain, but I could not get it without having my teeth set permanently right. And I knew those dentists; I knew they started fiddling about with all sorts of other teeth which had not yet begun to ache. They would not let sleeping dogs lie. If you gave them an inch they would take a mile.
"Now, if I may put it that way, our Lord is like the dentists. If you give Him an inch, He will take a mile. Dozens of people go to Him to be cured of some one particular sin which they are ashamed of... or which is obviously spoiling daily life (like bad temper or drunkenness). Well, He will cure it alright: but He will not stop there. That may be all you ask; but if once you call Him in, He will give you the full treatment. That is why He warned people to 'count the cost' before becoming Christians. 'Make no mistake,' He says, 'If you let me, I will make you perfect. The moment you put yourself in My hands, that is what you are in for. Nothing less or other than that.'
"'Whatever suffering it may cost you in your earthly life... whatever it cost Me, I will never rest, nor let you rest, until you are literally perfect--until my Father can say without reservation that He is well pleased with you, as He said He was well pleased with me. This I can do and will do. But I will not do anything less.'
"The goal toward which He is beginning to guide you is absolute perfection; and no power in the whole universe, except you yourself, can prevent Him from taking you to that goal. That is what you are in for. And it is very important to realize that. If we do not, then we are very likely to start pulling back and resisting Him after a certain point. I think that many of us, when Christ has enabled us to overcome one or two sins that were an obvious nuisance, are inclined to feel (though we do not put it into words) that we are now good enough. He has done all we wanted Him to do. And we should be obliged if He would now leave us alone.
"But this is the fatal mistake... The question is not what we intended ourselves to be, but what He intended us to be when He made us....
"Imagine yourself as a living house. God comes in to rebuild that house. At first, perhaps you can understand what He is doing. He is getting the drains right and stopping the leaks in the roof and so on: you know that those jobs needed doing and so you are not surprised. But presently he starts knocking the house about in a way that hurts abominably and does not seem to make sense. What on earth is He up to? The explanation is that He is building quite a different house from the one you thought of--throwing out a new wing here, putting on an extra floor there, running up towers, making courtyards. You thought you were going to be made into a decent little cottage: but He is building a palace. He intends to come and live in it Himself!"