15.  Nor must he suppose that the same things are suitable to all, just as all have not the same stature, nor are the features of the face, nor the nature of animals, nor the qualities of soil, nor the beauty and size of the stars, in all cases the same:  but he must consider base conduct a fault in a private individual, and deserving of chastisement under the hard rule of the law; while in the case of a ruler or leader it is a fault not to attain to the highest possible excellence, and always make progress in goodness, if indeed he is, by his high degree of virtue, to draw his people to an ordinary degree, not by the force of authority, but by the influence of persuasion.  For what is involuntary apart from its being the result of oppression, is neither meritorious nor durable.  For what is forced, like a plant A plant.  Cf. Orat. vi. 8, xxiii. 1.  A favourite figure of S. Gregory. violently drawn aside by our hands, when set free, returns to what it was before, but that which is the result of choice is both most legitimate and enduring, for it is preserved by the bond of good will.  And so our law and our lawgiver enjoin upon us most strictly that we should “tend the flock not by constraint but willingly.” 1 Pet. v. 2.