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. 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.” […]

Every father is pleased at the baby’s first attempt to walk: no father would be satisfied with anything less than a firm, free, manly walk in a grown-up son. In the same way, he said, “God is easy to please, but hard to satisfy.

~ C.S Lewis, Counting The Cost, Mere Christianity

Sometimes like to imagine that I can just see how it might apply to other things. I think I can see how the higher animals are in a sense drawn into Man when he loves them and makes them (as he does) much more nearly human than they would otherwise be. I can even see a sense in which the dead things and plants are drawn into Man as he studies them and uses and appreciates them. And if there were intelligent creatures in other worlds they might do the same with their worlds. It might be that when intelligent creatures entered into Christ they would, in that way, bring all the other things in along with them. But I do not know: it is only a guess.

~ C.S Lewis, Is Christianity Hard Or Easy?, Mere Christianity

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.”

~ C.S Lewis, Is Christianity Hard Or Easy?, Mere Christianity

The rule for all of us is perfectly simple. Do not waste time bothering whether you “love” your neighbour; act as if you did. As soon as we do this we find one of the great secrets. When you are behaving as if you loved someone, you will presently come to love him.

~ C.S Lewis, Charity, Mere Christianity