Moreover when you fast, be not, as the hypocrites, of a sad countenance: for they disfigure their faces, that they may appear unto men to fast. Verily I say unto you, They have their reward.
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Augustine of Hippo
There follows a precept concerning fasting, having reference to that same purification of heart which is at present under discussion. For in this work also we must be on our guard, lest there should creep in a certain ostentation and hankering after the praise of man, which would make the heart double, and not allow it to be pure and single for apprehending God.
It is manifest from these precepts that all our effort is to be directed towards inward joys, lest, seeking a reward from without, we should be conformed to this world, and should lose the promise of a blessedness so much the more solid and firm, as it is inward, in which God has chosen that we should become conformed to the image of His Son.
But in this section it is chiefly to be noticed, that there may be ostentatious display not merely in the splendour and pomp of things pertaining to the booty, but also in doleful squalor itself; and the more dangerous on this account, that it deceives under the name of serving God. And therefore he who is very conspicuous by immoderate attention to the body, and by the splendour of his clothing or other things, is easily convicted by the things themselves of being a follower of the pomps of the world, and misleads no one by a cunning semblance of sanctity; but in regard to him who under a profession of Christianity, fixes the eyes of men upon himself by unusual squalor and filth, when he does it voluntarily, and not under the pressure of necessity, it may be conjectured from the rest of his actings whether he does this from contempt of superfluous attention to the body, or from a certain ambition: for the Lord has enjoined us to beware of wolves under a sheep's skin; but by their fruits, says He, shall you know them. For when by temptations of any kind those very things begin to be withdrawn from them or refused to them, which under that veil they either have obtained or desire to obtain, then of necessity it appears whether it is a wolf in a sheep's skin or a sheep in its own. For a Christian ought not to delight the eyes of men by superfluous ornament on this account, because pretenders also too often assume that frugal and merely necessary dress, that they may deceive those who are not on their guard: for those sheep also ought not to lay aside their own skins, if at any time wolves cover themselves there with.