[88] [cap.14] But, there being three leaders and authors of this race, the two at each extremity of it had their names changed, namely Abraham and Jacob: but the one in the middle, Isaac, always retained the same appellation. Why was this? Because both that virtue which is derived from teaching and that which is attained to by practise, admit of improvement and advancement: for the man who receives instruction desires a knowledge of those matters of which he is ignorant and he who applies himself to practise desires the crowns of victory, and the prizes which are proposed to his industrious and contemplation-loving soul. But the race which is self-taught and which derives all its learning from its own diligence, inasmuch as it exists rather by nature than by study, was at the very beginning introduced as equal, and perfect, and even, there being no number whatever deficient of those which tend to completeness.