Psalms 63:2

"My soul hath thirsted for Thee" (ver. 2). Behold that desert of Idumaea. See how here he thirsteth: but see what good thing is here, "Hath thirsted for Thee." For there are they that thirst, but not for God. For every one that willeth anything to be granted to him, is in the heat of longing; the longing itself is the thirst of the soul. And see ye what longings there are in the hearts of men: one longeth for gold, another longeth for silver, another longeth for possessions, another inheritance, another abundance of money, another many herds, another a wife, another honours, another sons. Ye see those longings, how they are in the hearts of men. All men are inflamed with longing, and scarce is found one to say, "My soul hath thirsted for Thee." For men thirst for the world: and perceive not themselves to be in the desert of Idumaea, where their souls ought to thirst for God. ...Wisdom therefore must be thirsted after, righteousness must be thirsted after. With it we shall not be satisfied, with it we shall not be filled, save when this life shall have been ended, and we shall have come to that which God hath promised. For God hath promised equality with Angels: and now the Angels thirst not as we do, they hunger not as we do; but they have the fulness of truth, of light, of immortal wisdom. Therefore blessed they are, and out of so great blessedness, because they are in that City, the Heavenly Jerusalem, afar from whence we now are sojourning in a strange land, they observe us sojourners, and they pity us, and by the command of the Lord they help us, in order that to this common country sometime we may return, and there with them sometime with the Lord's fountain of truth and eternity we may be filled. Now therefore let our soul thirst: whence doth our flesh also thirst, and this in many ways? "In many ways for Thee," he saith, "my flesh also." Because to our flesh also is promised Resurrection. As to our soul is promised blessedness, so also to our flesh is promised resurrection. ...Observing what a hope of resurrection God promiseth to us, in all those our manifold faintings we thirst for that incorruption: and so our flesh manifoldly doth thirst for God. Nevertheless, my brethren, the flesh of a good Christian and a believer even in this world for God doth thirst: for if the flesh hath need of bread, if it hath need of water, if it hath need of wine, if it hath need of money, if this flesh hath need of a beast, from God it ought to seek it, not from demons and idols and I know not what powers of this world. ...But they that thirst for God, everywhere ought to thirst for Him, both soul and flesh: for to the soul also God giveth His bread, that is the Word of Truth: and to the flesh God giveth the things which are necessary, for God hath made both soul and flesh. ...He that hath made the soul, the Same hath made the flesh also: He that hath made both of them, the Same feedeth both of them. Let either part of us thirst for God, and after labour manifold let either simply be filled.

Therefore God gave us a pattern of fasting in this deed, so that having a desert, as it were, at the time of fasting we may abstain from feasts, pleasure and women, and so that Eve may not be joined with us so as to subvert us from chaste observance by her alluring persuasion. For he who fasts and is chaste at the time of the 40-day fast seems somehow to dwell in the desert. Clearly, that certain desert is the body of a Christian when it is not filled with food or watered with drinks, but is neglected by the squalor of thirsty starvation. The desert, I say, is our body when the flesh begins to grow weaker by abstinence, when pallor is overcome by thirst, and the unadorned appearance of the whole human being becomes dirty by the contempt of material things. Then Christ the Lord dwells in the desert of our body, when he has discovered our land squalid in hunger and dry by thirst, just as that adage which the prophet David says, "Just like in a deserted land where there are neither roads nor water, so I appeared in your sanctuary." For we are not able to appear to him in the sanctuary in any other way, unless the land of our body has been made desert from worldly delights and without the roads made by devilish desires and without the water from libidinous allurements. Then the Savior, dwelling in this desert of our body, conquers all the factions of the devil and makes our body his own dwelling, safe and secure from the thoughts of this age, so that we may be constituted in solitude within our very selves, as it were, and see nothing but heaven and earth. That is to say, we think about nothing other than the Lord of the heavenly kingdom and the author of the earthly resurrection.