But how shall we not acknowledge the highest gratitude to the divine Instructor, who is not silent, who omits not those threatenings that point towards destruction, but discloses them, and cuts off the impulses that tend to them; and who indoctrinates in those counsels which result in the true way of living? We must confess, therefore, the deepest obligations to Him. For what else do we say is incumbent on the rational creature--I mean man--than the contemplation of the Divine? I say, too, that it is requisite to contemplate human nature, and to live as the truth directs, and to admire the Instructor and His injunctions, as suitable and harmonious to each other. According to which image also we ought, conforming ourselves to the Instructor, and making the word and our deeds agree, to live a real life. CHAPTER XIII. VIRTUE RATIONAL, SIN IRRATIONAL. Everything that is contrary to right reason is sin. Accordingly, therefore, the philosophers think fit to define the most generic passions thus: lust, as desire disobedient to reason; fear, as weakness disobedient to reason; pleasure, as an elation of the spirit disobedient to reason. If, then, disobedience in reference to reason is the generating cause of sin, how shall we escape the conclusion, that obedience to reason--the Word--which we call faith, will of necessity be the efficacious cause of duty? For virtue itself is a state of the soul rendered harmonious by reason in respect to the whole life. Nay, to crown all, philosophy itself is pronounced to be the cultivation of right reason; so that, necessarily, whatever is done through error of reason is transgression, and is rightly called (ἁμάρτημα) sin. Since, then, the first man sinned and disobeyed God, it is said, “And man became like to the beasts:”[414] being rightly regarded as irrational, he is likened to the beasts. Whence Wisdom says: “The horse for covering; the libidinous and the adulturer is become like to an irrational beast.”[415] Wherefore also it is added: “He neighs, whoever may be sitting on him.” The man, it is meant, no longer speaks; for he who transgresses against reason is no longer rational, but an irrational animal, given up to lusts by which he is ridden (as a horse by his rider).