Plato, Letters 314a

καὶ θεοφιλεστέραν. εὐλαβοῦ μέντοι μή ποτε ἐκπέσῃ ταῦτα εἰς ἀνθρώπους ἀπαιδεύτους· σχεδὸν γάρ, ὡς ἐμοὶ δοκεῖ, οὐκ ἔστιν τούτων πρὸς τοὺς πολλοὺς καταγελαστότερα ἀκούσματα, οὐδʼ αὖ πρὸς τοὺς εὐφυεῖς θαυμαστότερά τε καὶ ἐνθουσιαστικώτερα. πολλάκις δὲ λεγόμενα καὶ ἀεὶ ἀκουόμενα καὶ πολλὰ ἔτη, μόγις ὥσπερ χρυσὸς ἐκκαθαίρεται μετὰ πολλῆς πραγματείας. ὃ δὲ θαυμαστὸν αὐτοῦ γέγονεν, ἄκουσον. εἰσὶν γὰρ ἄνθρωποι ταῦτα ἀκηκοότες καὶ πλείους, δυνατοὶ

Beware, however, lest these doctrines be ever divulged to uneducated people. For there are hardly any doctrines, I believe, which sound more absurd than these to the vulgar, or, on the other hand, more admirable and inspired to men of fine disposition. For it is through being repeated and listened to frequently for many years that these doctrines are refined at length, like gold, with prolonged labor. But listen now to the most remarkable result of all. Quite a number of men there are