For if this, through separate attacks made at random, and by haphazard and casual changes, has secured an opportunity of gaining possession of our mind, it keeps us back at all times from all insight in divine contemplation, and utterly ruins and depresses the mind that has fallen away from its complete state of purity.
It does not allow it to say its prayers with its usual gladness of heart, nor permit it to rely on the comfort of reading the sacred writings, nor suffer it to be quiet and gentle with the brethren;
it makes it impatient and rough in all the duties of work and devotion: and, as all wholesome counsel is lost, and steadfastness of heart destroyed, it makes the feelings almost mad and drunk, and crushes and overwhelms them with penal despair.
Wherefore if we are anxious to exert ourselves lawfully in the struggle of our spiritual combat we ought with no less care to set about healing this malady also. For “as the moth injures the garment, and the worm the wood, so dejection the heart of man.”
With sufficient clearness and appropriateness has the Divine Spirit expressed the force of this dangerous and most injurious fault. For the garment that is moth-eaten has no longer any commercial value or good use to which it can be put; and in the same way the wood that is worm-eaten is no longer worth anything for ornamenting even an ordinary building, but is destined to be burnt in the fire.
So therefore the soul also which is a prey to the attacks of gnawing dejection will be useless for that priestly garment which, according to the prophecy of the holy David, the ointment of the Holy Spirit coming down from heaven, first on Aaron’s beard, then on his skirts, is wont to assume: as it is said, “It is like the ointment upon the head which ran down upon Aaron’s beard, which ran down to the skirts of his clothing.”
Nor can it have anything to do with the building or ornamentation of that spiritual temple of which Paul as a wise master builder laid the foundations, saying, “Ye are the temple of God, and the Spirit of God dwelleth in you:” and what the beams of this are like the bride tells us in the Song of Songs: “Our rafters are of cypress: the beams of our houses are of cedar.”
And therefore those sorts of wood are chosen for the temple of God which are fragrant and not liable to rot, and which are not subject to decay from age nor to be worm-eaten.
John Cassian (c. 360-435): Institutes 9, 1-3.