Commentary on the First Alcibiades of Plato (Cambridge, University Library, MS Kk.5.27)

first, regarding the immortality of the soul and its eternity, and reasonably so. For in this dialogue, he discusses knowing oneself. And we know ourselves by turning back toward ourselves. And it has been shown by the philosophers with a thousand lines that everything which turns back upon itself is eternal and immortal; we shall know here, therefore, that the soul is immortal. Second, it contributes to the knowledge of all things that exist. For if we know the soul, we shall also know whatever it contains the reasons original: "λόγους" of within itself. And it contains the reasons and types of all things that exist, being an image of them. Therefore, the knowledge of the soul contributes to the knowledge of all things that exist. Third, it helps us know what is good for the soul and what is bad. For just as if man were a mouth, his perfection would be size and beauty; if he were spirit, his perfection would be ambition; if he were desire, it would be the love of pleasure; so, since he is reason, that is, a rational soul, virtue is sufficient for him for happiness, and vice for misery. For as Plato says, the soul will depart to Hades having nothing except virtue and vice. This is the usefulness. But concerning practice...