There are three virtues which bestow light on the intellect at all times: knowing no evil against anyone, doing good to those who wrong you, and enduring calmly the things which come your way.
These three virtues give rise to another three which are still greater: knowing no evil against anyone gives rise to love, doing good to those who wrong you produces peace, and enduring calmly the things which come your way brings meekness.
There are four virtues which purify the soul: silence, keeping the commandments, <spiritual> constraint and humility.
The intellect always needs the following four virtues: praying to God by constantly prostrating oneself before him, surrendering before God, being unconcerned with everyone in order not to judge, and being deaf to the passions which speak to it.
Four virtues fortify the soul, allowing it to breathe from the disturbance of the enemy: mercy, freedom from anger, long-suffering, and shaking off every seed coming from sin. Resisting forgetfulness protects all of these.
There are four virtues which, after God Himself, assist the beginner: constant study, resoluteness, vigil and disregard for oneself.
[Abba Isaiah of Scetis, Ascetical Discourses, Discourse 7]