No man can conquer the passions except by the palpable virtues; and no one can conquer the wandering of the intellect except by the study of spiritual knowledge. Our intellect is volatile, and if it is not tied down by some reflection, it never stops wandering. Without attaining perfection in the aforesaid virtues, a man cannot acquire this safeguard. For unless a man does not vanquish his enemies, he cannot be at peace. And if peace does not reign, how can a man find those things that are stored up within peace? The passions are a wall impeding the hidden virtues of the soul. If the passions are not first cast down by means of externally manifest virtues, that which lies within cannot be seen; for a man who is outside a wall cannot keep company with what is inside. No man sees the sun in a cloud, nor the natural virtue of the soul in the constant turbulence of the passions.
Entreat God to give you to feel spiritual aspiration and yearning. For whenever this yearning of spirit comes upon you, you will stand aloof from the world and the world will stand aloof from you. It is, however, impossible to experience this without stillness, ascetic endeavor, and the converse of reading devoted to the same. Without the latter, do not seek the former; for if you seek after it, it will gradually be altered and become corporeal. Let him who has understanding understand. It was the wise Lord’s good pleasure that we should eat this bread with the sweat of our brow. He did not ordain this spitefully, but lest it should oblige us to vomit and we die. For every virtue is the mother of a second. If, then, you abandon the mother which gives birth to the virtues and go out to seek the daughters before you have acquired their mother, those virtues will be vipers to your soul, and if you do not hurl them away from you, speedily you will die.
St. Isaac the Syrian,The Ascetical Homilies of Saint Isaac the Syrian (I, 34), translated by the Holy Transfiguration Monastery, Boston, 1984. p. 157