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. You have free will, and if you choose, you can push Me away. But if you do not push Me away, understand that I am going to see this job through. Whatever suffering it may cost you in your earthly life, whatever inconceivable purification it may cost you after death, whatever it costs 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.'
And yet - this is the other and equally important side of it - this Helper who will, in the long run, be satisfied with nothing less than absolute perfection will also be delighted with the first feeble, stumbling effort you make tomorrow to do the simplest duty.
C.S. Lewis, Mere Christianity, pp. 202-203