"There are, then, many reasons why mortification is necessary. A further important consideration is that our facility in prayer largely depends on it, since without some kind of systematic self-denial we cannot pray well. And why? Because we cannot have close union with God unless we fulfill the conditions laid down by Himself, and one of these was that we should take up our cross daily. But another reason for it is that self-indulgence is the enemy of fervor, and it also fills the mind with distracting images, and the heart with counter-attractions, both of which prevent prayer. Indeed, so true is this connection between mortification and prayer that one spiritual master has roundly declared: 'There is a definite connection between how we take our food and how we pray.' We know, too, that mortification has the effect of producing peace of mind, largely because it strengthens the power of the will over the passions. That is one of several reasons why the most mortified individuals or communities are usually the most contented and cheerful, whereas the self-indulgent are generally restless and unhappy."
-Dom Basil Hemphill, OSB