“…see, at any rate how many blessings spring from both fasting and prayer. For he that is praying as he should, and is fasting as he should has not many wants, and he that has not many wants cannot be covetous; he that is not covetous will be also more disposed for almsgiving. He that fasts is light and prays with wakefulness and quenches his wicked lusts and propitiates God and humbles his soul when lifted up. Therefore even the apostles were not always fasting for the honor of fasting consists not in abstinence from food but in withdrawing from sinful practices.
Do you fast? Give me proof of it by your works!
By itself abstinence from food does not contribute to perfect purity of soul unless the other virtues are active as well. Humility, for example, practiced through obedience in our work and through bodily hardship, is a great help. Freedom from anger, from dejection, self-esteem and pride also contributes to purity of soul in general, while self-control and fasting are especially important for bringing about that specific purity of soul which comes through restraint and moderation.
Our initial struggle therefore must be to gain control of our stomach and to bring our body into subjection not only through fasting, but also through vigils, labors and spiritual reading,and through concentrating our heart on, and longing for the kingdom of heaven.”
(St. John Cassian, Philokalia Book One and St. John Chrysostom, The Gospel of Matthew from Emily Harakas, Through the Year with the Church Fathers, pp. 96 & 97)