If there lurks in most modern minds the notion that to desire our own good and earnestly to hope for the enjoyment of it is a bad thing, I submit that this notion has crept in from Kant and the Stoics, and is no part of Christian faith.
Indeed, if we consider the unblushing promises of reward and the staggering nature of the rewards promised in the Gospels, it would seem that Our Lord finds our desires not too strong, but too weak.
We are half-hearted creatures, fooling about with drink and sex and ambition when infinite joy is offered us, like an ignorant child who wants to go on making mud pies in a slum because he cannot imagine what is meant by the offer of a holiday at the sea. We are far too easily pleased.
“We must not be troubled by unbelievers when they say that this promise of reward makes the Christian life a mercenary affair. There are different kinds of rewards.
There is the reward which has no natural connection with the things you do to earn it and is quite foreign to the desires that ought to accompany those things. Money is not the natural reward of love; that is why we call a man mercenary if he marries a woman for the sake of her money. But marriage is the proper reward for a real lover, and he is not mercenary for desiring it…
The schoolboy beginning Greek grammar cannot look forward to his adult enjoyment of Sophocles as a lover looks forward to marriage or a general to victory. He has to begin by working for marks, or to escape punishment, or to please his parents, or, at best, in the hope of a future good which he cannot at present imagine or desire. His position, therefore, bears a certain resemblance to that of the mercenary; the reward he is going to get will, in actual fact, be a natural or proper reward, but he will not know that till he has got it….
“The Christian, in relation to heaven, is in much the same position as this schoolboy. Those who have attained everlasting life in the vision of God doubtless know very well that it is no mere bribe, but the very consummation of their earthly discipleship; but we who have not yet attained it cannot know this in the same way, and cannot even begin to know it at all except by continuing to obey and finding the first reward of our obedience in our increasing power to desire the ultimate reward.”
- C.S. Lewis, The Weight of Glory (First American Edition, Macmillan, 1949), pp. 1–3.