Taken from the writing of George Smith:
Christianity cannot erase man's need for pleasure, nor can it eradicate the various sources of pleasure. What it can do, however, and what it has been extremely effective in accomplishing, is to inculcate guilt in connection with pleasure. The pursuit of pleasure, when accompanied by guilt, becomes a means of perpetuating chronic guilt, and this serves to reinforce one's dependence on God.
Christianity, with some exceptions, has never explicitly advocated human misery; it prefers instead to speak of sacrifices in this life so that benefits may be garnered in the life to come. One invests in this life, so to speak, and collects interest in the next. Fortunately for Christianity, the dead cannot return for a refund.
Through inculcating the notion that sacrifice is a virtue, Christianity has succeeded in convincing many people that misery incurred through sacrifice is a mark of virtue. Pain becomes the inignia of morality - and conversely, pleasure becomes the insignia of immorality. Christianity, therefore, does not say, "Go forth and be miserable". Rather, it says, "Go forth and practice the virtue of self-sacrifice". In practical terms, these commands are identical.
In exchange for obedience, Christianity promises salvation in an afterlife; but in order to elicit obedience through this promise, Christianity must convince men that they need salvation, that there is something to be saved from. Christianity has nothing to offer a happy man living in a natural, intelligible universe. If Christianity is to gain a motivational foothold, it must declare war on earthly pleasure and happiness, and this, historically, has been its precise course of action. In the eyes of Christianity, man is sinful and helpless in the face of God, and is potential fuel for the flames of hell. Just as Christianity must destroy reason before it can introduce faith, so it must destroy happiness before it can introduce salvation.