Here is one of my favorite passages from C. S. Lewis's Mere Christianity, in which he talks about how Christianity is both harder and easier than trying to be a moral person, while preserving the natural self.
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 get angrier and angrier. In the end, you 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 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. (Mere Christianity, p. 196-197)