“The ordinary idea which we all have before we become Christians is this. We take as a starting point our ordinary self with its various desires and interests. We then admit that something else—call it ‘morality’ or ‘decent behavior’ or ‘the good of society’—has claims on this self; claims which interfere with its own desires. What we mean by ‘being good’ is giving in to those claims. Some of the things the ordinary self wanted to do turn out to be what we call ‘wrong’: well, we must give them up. Other things, which the self did not want to do, turn out to be what we call ‘right’: well, we shall have to do them. But we are hoping all the time that when all the demands have been met, the poor natural self will still have some chance, and some time, to get on with its own life and do what it likes. In fact, we are very like an honest man paying his taxes. He pays them all right, but he does hope that there will be enough left over for him to live on. Because we are still taking our natural self as the starting point.
As long as we are thinking that way, one or other of two results is likely to follow. Either we give up trying to be good, or else we become very unhappy indeed. For, make no mistake: if you are really going to try to meet all the demands made on the natural self, it will not have enough left over to live on. The more you obey your conscience, the more your conscience will demand of you. And your natural self, which is thus being starved and hampered and worried at every turn, will either give up trying to be good, or else become one of those people who, as they say, “live for others” but always in a discontented, grumbling way—always wondering why the others do not notice it more, and always making a martyr out of yourself. And once you have become that you will be a far greater pest to anyone who has to live with you than you would have been if you had remained frankly selfish.
The Christian way is different: harder, and easier. 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.”
-taken from Mere Christianity