Plato, Laws 835c

ἃ δὲ μὴ σμικρὸν διαφέρει, πείθειν τε χαλεπόν, θεοῦ μὲν μάλιστα ἔργον, εἴ πως οἷόν τε ἦν ἐπιτάξεις αὐτὰς παρʼ ἐκείνου γίγνεσθαι, νῦν δὲ ἀνθρώπου τολμηροῦ κινδυνεύει δεῖσθαί τινος, ὃς παρρησίαν διαφερόντως τιμῶν ἐρεῖ τὰ δοκοῦντα ἄριστʼ εἶναι πόλει καὶ πολίταις, ἐν ψυχαῖς διεφθαρμέναις τὸ πρέπον καὶ ἑπόμενον πάσῃ τῇ πολιτείᾳ τάττων, ἐναντία λέγων ταῖς μεγίσταισιν ἐπιθυμίαις καὶ οὐκ ἔχων βοηθὸν ἄνθρωπον οὐδένα, λόγῳ ἑπόμενος μόνῳ μόνος.

gain or loss to the State. But the things which do make no small difference, and of which it is hard to persuade men—these form a task especially for God (were it possible that orders should come from him): as it is, they are likely to require a bold man who, valuing candor above all else, will declare what he deems best for city and citizens, and in the midst of corrupted souls will enjoin what is fitting and in keeping with all the constitution, and gainsay the mightiest lusts, acting alone by himself with no man to help him save, as his solitary leader, Reason.