In truth those who have the skill properly to direct and heal rational souls are rare, and especially at the present time. Many, perhaps, have made a pretense of fasting and vigil and a form of godliness… As for learning many things by heart and teaching them in words, this is easy for most men, but as for eliminating the passions and acquiring the capital virtues so that they cannot be lost, very few are found [who do this]. Now we call "capital virtues" humility, which eliminates the passions and obtains heavenly and angelic impassibility, and love, which never ceases or fails (cf. 1 Cor. 13:8) but continually presses on to that which lies ahead (cf. Phil. 3:13-14) as it adds desire to desire and love to love. It supplies perfect discernment, and by itself is a good guide to those who follow after it and infallibly carries us across the spiritual sea… Do not follow the wolf instead of the shepherd (cf. Mt. 7:15), nor enter into a flock that is diseased (cf. Ezek. 34:4).
(Saint Symeon the New Theologian)