The natural life in each of us is something self-centered, something that wants to be petted and admired, to take advantage of other lives, to exploit the whole universe. And especially it wants to be left to itself: to keep well away from anything better or stronger or higher than it, anything that might make it feel small. It is afraid of the light and air of the spiritual world. ...It knows that if the spiritual life gets hold of it, all its self-centeredness and self will are going to be killed and it is ready to fight tooth and nail to avoid it.We are ready to fight tooth and nail to keep secret all the things we don't want Jesus to root out. But, he must. And...
...the business of becoming a son of God, of being turned from a created thing into a begotten thing, of passing over from the temporary biological life into a timeless "spiritual" life has been done for us [through Jesus].Lewis goes on to say that we must get close to him and as we do "we shall catch it," catch the "infection" of salvation and grace. The challenge of Christmas is to get close enough to wonder in the incarnation and not mistaken it as trite.
(Both citations are taken from Mere Christianity, chapter 5.)