Do you want to know how much fasting adorns human beings; how much she defends and secures us from danger? I beg of you, think of the blessed and marvelous race of the monastics. In other words, they took flight from the tumult in their midst and they ran quickly to the peaks of the mountains; they erected their huts in the solitude of the desert as if they pitched them in a sheltered harbour; and they took fasting as a companion and joint communicant throughout their entire lives. This is why she made them angels from men; not only them, but as many as she finds in the cities that submit to her, she elevates to the same height of the wisdom of God.
Likewise Moses and Elijah, the pillars of the prophets in the Old Testament – although they were brilliant and great from their other virtues and courageous in approaching God and conversing with Him, as much as is humanly possible – fled for refuge to fasting, and with her power they approached Him.
For this reason, God, when in the beginning he created man, He immediately brought him over to and deposited him in the hands of fasting; and he entrusted his salvation to her as if to a loving mother and an excellent teacher. Because the command: “Of every tree which is in the garden you may freely eat, but of the tree of knowledge of good and evil, of it you shall not eat” (Gen 2.16) was one kind of fasting. If fasting was imperative in paradise, much more so was it outside of paradise. If the medicine was useful before the wound, much more so was it after the wound. If the weapon was necessary for us before the rising of the war of the passions and the tremendous battle with the demons, much more so will the defense of fasting be indispensable. If Adam had heard the voice (Gen 2.16), he would not have heard the second one, which said: “You are earth, and to earth you shall return” (Gen 3.20). However since he disobeyed that voice, death, anxieties, toils, faintheartedness, and a life that is altogether more burdensome than death came upon the human race; this is why thorns and thistles came about, this is the reason for the labours and pains and a life weary with toil.
[St. John Chrysostom, On Fasting and the Prophet Jonah, [the Prophet] Daniel and the Three Youths]