From Samuel Johnson’s Life of Milton:
But the truth is, that the knowledge of external nature, and the sciences which that knowledge requires or includes, are not the great or the frequent business of the human mind. Whether we provide for action or conversation, whether we wish to be useful or pleasing, the first requisite is the religious and moral knowledge of right and wrong; the next is an acquaintance with the history of mankind, and with those examples which may be said to embody truth, and prove by events the reasonableness of opinions. Prudence and justice are virtues and excellences of all times and of all places; we are perpetually moralists, but we are geometricians only by chance. Our intercourse with intellectual nature is necessary; our speculations upon matter are voluntary, and at leisure. Physiological learning is of such rare emergence, that one may know another half his life without being able to estimate his skill in hydrostatics or astronomy; but his moral and prudential character immediately appears.
Those authors, therefore, are to be read at schools that supply most axioms of prudence, most principles of moral truth, and most materials for conversation; and these purposes are best served by poets, orators, and historians.
Let me not be censured for this digression as pedantic or paradoxical; for, if I have Milton against me, I have Socrates on my side. It was his labour to turn philosophy from the study of Nature to speculations upon life; but the innovators whom I oppose are turning off attention from life to nature. They seem to think that we are placed here to watch the growth of plants, or the motions of the stars. Socrates was rather of opinion that what we had to learn was how to do good and avoid evil.
ὅττι τοι ἐν μεγάροισι κακόν τ᾽ ἀγαθόν τε τέτυκται
The quote is from Book 4 of The Odyssey (~400), as Eidothea instructs a stranded Menelaus in how to catch her father Proteus:
τόν γ᾽ εἴ πως σὺ δύναιο λοχησάμενος λελαβέσθαι,
ὅς κέν τοι εἴπῃσιν ὁδὸν καὶ μέτρα κελεύθου
νόστον θ᾽, ὡς ἐπὶ πόντον ἐλεύσεαι ἰχθυόεντα.
καὶ δέ κέ τοι εἴπῃσι, διοτρεφές, αἴ κ᾽ ἐθέλῃσθα,
ὅττι τοι ἐν μεγάροισι κακόν τ᾽ ἀγαθόν τε τέτυκται
οἰχομένοιο σέθεν δολιχὴν ὁδὸν ἀργαλέην τε.
If you could somehow lie in wait and catch him, he will tell you your way and the measure of your path, and of your return, how you may go over the fish-filled sea. And he will tell you, fostered by Zeus, if so you wish, what evil and what good has been done in your halls, while you have been gone on your long and grievous way.