At that time, Jesus said to his disciples: “When you fast, do not look gloomy like the hypocrites.” (Mt 6:16-21)
Homily of St Augustine
(Book 2 on the Lord’s Sermon on the Mount, Vol. 4, Ch. 12)
It is clear from these precepts that all our efforts should be directed toward achieving internal joy, lest in seeking an external reward we may be so conformed to the spirit of this world, that we disregard the promise of that happiness which is the more substantial and lasting because it is interior. It is in that happiness God has chosen we be made in the likeness of his Son.
In this chapter the point will be made that it is possible to be vainglorious not only of the pomp and splendour of earthly possessions, but even of squalid poverty. This last is more dangerous, because it is done under the name of serving God.
The man, therefore, who makes himself conspicuous through excessive care of the body, of dress, or display of other sorts, by these very things is proved to be a follower of worldly vanities. He deceives no one by his mask of holiness.
But the man who is parading his Christianity causes the eyes of all men to turn towards him by his eccentric display of groveling and dirtiness – a state which he endures not from necessity but of his own choice – must be judged from his other actions whether he bears this state through the virtue of mortification in the giving up of unnecessary comfort, or from an ostentatious vanity. The Lord bids us beware of wolves in sheep’s clothing. “By their fruits,” he says, “you shall know them.”
When various trials come upon these persons and they lose or are denied those things, which under the guise of spirituality, they gained, or at least they strove to gain, then it becomes apparent whether they are wolves in sheep’s clothing, or sheep in their own.
Nevertheless, a Christian should not attract attention with needless display, because hypocrites, feigning poor and mean attire, sometimes deceive the guileless. Nor should sheep cast away their own clothing because wolves sometimes assume it.
– From: An Approved English Translation of the Breviarium Romanum, Burns & Oates, London, 1964