Letter 221: Advice given seems like a warning.

To Primos. What it means that Peter cut off the ear of the high priest's servant. He who conducts himself in the company of Jesus, and who keeps his mind following after Jesus, defends his Teacher when He is blasphemed, as Peter did. For since the Jews yielded a disobedient ear, not even heeding the Law so as to listen, in all things whatsoever Christ should speak, to Him as He taught, Peter cut off the ear of the household slave who belonged to the priest [the high priest's servant, John 18:10] -- thereby showing that the priest was a slave to the Law's disobedience, and that he stood in need of a sword for the cutting away of his gainsaying.

Τί σημαίνει τό, ἀποκόψαι Πέτρου τοῦ δούλου τοῦ ἀρχιερέως τὸ ὠτίον. Ὁ μετὰ Ἰησοῦ ἀναστρεφόμενος, καὶ ἀκολουθήσαν ἔχων τῷ Ἰησοῦ τὴν διάνοιαν, ἀμύνει βλασφημουμένῳ τῷ Διδασκάλῳ, ὡς Πέτρος, [ὃς] ἐπειδὴ ἀνήκοαν ἐνδοῦσαν Ἰουδαῖοι, οὐδὲ τῷ νόμῳ προσέχοντες ἀκούειν κατὰ πάντα ὅσα Χριστὸς λαλήσει διδάσκοντι, τὸ οὖς τοῦ οἰκέτου ἀπέτεμε, τοῦ τῷ ἱερεῖ διαφέροντος, δοῦλον εἶναι τῆς ἀπειθείας τοῦ νόμου τὸν ἱερέα δηλῶν, καὶ χρήζοντα μαχαίρας εἰς ἀποτομὴν τῆς ἀντιλογίας.