Letter 456: Do not think you need only to be above reproach, Arabianus.

To Arabianus the Bishop. The man who cannot teach, but is willing to learn, is worthy of acceptance. But the man who, besides not knowing, also professes to teach, sick with the utmost want of learning, will not even be able to learn, since his appearing to know leaves no room for it.

Ὁ διδάσκειν μὲν μὴ δυνάμενος, μαθεῖν δὲ βουλόμενος ἀποδοχῆς ἐστιν ἄξιος. Ὁ δὲ πρὸς τῷ μὴ εἰδέναι καὶ διδάσκειν ἐπαγγελλόμενος, ἐσχάτην ἀπαιδευσίαν νοσῶν, οὐδὲ μαθεῖν δυνησεται, τοῦ δοκεῖν εἰδέναι χώραν μὴ παρέχοντος.