From The Catholic Encyclopaedia‘s article on free will by Michael Maher (1909):
“Our moral freedom, like other mental powers, is strengthened by exercise. The practice of yielding to impulse results in enfeebling self-control. The faculty of inhibiting pressing desires, of concentrating attention on more remote goods, of reinforcing the higher but less urgent motives, undergoes a kind of atrophy by disuse. In proportion as a man habitually yields to intemperance or some other vice, his freedom diminishes and he does in a true sense sink into slavery. He continues responsible in causa for his subsequent conduct, though his ability to resist temptation at the time is lessened. On the other hand, the more frequently a man restrains mere impulse, checks inclination towards the pleasant, puts forth self-denial in the face of temptation, and steadily aims at a virtuous life, the more does he increase in self-command and therefore in freedom. The whole doctrine of Christian asceticism thus makes for developing and fostering moral liberty, the noblest attribute of man. William James’s sound maxim: “Keep the faculty of effort alive in you by a little gratuitous exercise every day”, so that your will may be strong to stand the pressure of violent temptation when it comes, is the verdict of the most modern psychology in favour of the discipline of the Catholic Church.”
Before reading this, the idea of asceticism had never made sense to me. It seemed like an odd, backward thing – much like the depiction of the camp of Christians in Brave New World – irrational.
Yet, with this it suddenly makes sense. Will power is like a muscle – it increases with increased use. Asceticism is basically a training course for the muscle of will power. The end goal (among others) is therefore to create a freedom – to amplify free will through a developed will power.
(Not surprisingly, then, the word asceticism comes from the Greek askesis which means practice, bodily exercise, and more especially, athletic training.)
Contrariwise, the lack of an ascetic sense in significant parts of contemporary society (and instead the cultivation of ‘mere impulse’, as seen through much advertising, say) means that many people have lost a significant amount of freedom in an important sense.
So, asceticism in reality is primarily a constructive practice: the point is to create more will power, which when combined with free will allows one to choose the right or the good more often (such as long-term good over short-term good).
Also see here.