Harmony sinks deep into the recesses of the soul and takes its strongest hold there, bringing grace also to the body & mind as well. Music is a moral law. It gives a soul to the universe, wings to the mind, flight to the imagination, a charm to sadness, and life to everything. It is the essence of order.
.. we shall not be properly educated ourselves, nor will the guardians whom we are training, until we can recognise the qualities of discipline, courage, generosity, greatness of mind, and others akin to them, as well as their opposites in all their manifestations.
The true lover of learning then must his earliest youth, as far as in him lies, desire all truth.... He whose desires are drawn toward knowledge in every form will be absorbed in the pleasures of the soul, and will hardly feel bodily pleasures I mean, if he be a true philosopher and not a sham one ... Then how can he who has the magnificence of mind and is the spectator of all times and all existence, think much of human life He cannot. Or can such a one account death fearful No indeed.
The cause of all the blunders committed by man arises from this excessive self-love. For the lover is blinded by the object loved; so that he passes a wrong judgment on what is just, good and beautiful, thinking that he ought always to honor what belongs to himself in preference to truth. For he who intends to be a great man ought to love neither himself nor his own things, but only what is just, whether it happens to be done by himself, or by another.
What the expression is intended to mean, I think, is that there is a better and a worse element in the character of each individual, and that when the naturally better element controls the worse then the man is said to be "master of himself", as a term of praise. But when - as a result of bad upbringing or bad company one s better element is overpowered by the numerical superiority of one s worse impulses, then one is criticized for not being master of oneself and for lack of self control.