Fasting protects all virtues. It is the beginning of spiritual struggle, the crown of those who refrain themselves, the beauty of virginity and purity, the brilliance of wisdom, the beginning of the Christian life, the mother of prayer, the spring of abstinence and thrift. It teaches us about serenity and precedes all good deeds (Saint Isaac the Syrian).

Since we are tempted through all our senses, we shall guard them through abstinence. Thus, what is the use of fasting if you abstain yourself from food but your eyes make you sin in the bottom of your soul and you are tempted by the sinful eye, if your hearing receives curses, shameful songs and evil speaking and you receive things that hurt the other senses? None, of course. (St. Gregory Palamas)

Therefore, this is how you should be fasting. First of all, keeping yourself away from any mean words and clean your heart from all worldly temptations. If you will pay attention to these, this fasting will be complete. You will do as it follows. After you will fulfil what was written above, you will taste nothing else but bread and water. And from your food that you wanted to eat you will make an estimation and give it to the widows and orphans, or to whoever is in need. Thus, your spirit will be humble because those who have received mercy from you will pray to God for you. So, if you will fast as I have taught you, your sacrifice will be received by God. (The Shepherd of Hermas)

Staying away from food is not enough when you are fasting, therefore we shall fast as God wants. The true fasting means keeping yourself far from all evil, anger, gossip, passions and lies. This is what can be considered a true fast. (Saint Basil the Great)

Do not refrain yourself only from bread and wine and meat and fine drinks but also from evil thoughts. (St. Nilus the Ascetic)

This is the true understanding of fasting, manifesting it through all good deeds. Do not feed you mind with wicked pleasures. (St. Cyril of Alexandria)

True fasting is the separation of all evil (St. Theodore of Studios)

(Translation from Simeon Koutsas, Postul Bisericii. De ce, când și cum postim, Apostoliki Diakonia, Atena, 2011)