Initiation

Diodorus Siculus
Library of History, Book V, 49.5-6

[5.49.5]
καὶ τὰ μὲν κατὰ μέρος τῆς τελετῆς ἐν ἀπορρήτοις τηρούμενα μόνοις παραδίδοται τοῖς μυηθεῖσι· διαβεβόηται δʼ ἡ τούτων τῶν θεῶν ἐπιφάνεια καὶ παράδοξος ἐν τοῖς κινδύνοις βοήθεια τοῖς ἐπικαλεσαμένοις τῶν μυηθέντων.

[5.49.5] The details of the initiatory rite are guarded among those matters which must not be revealed and are only communicated to the initiated; nevertheless the fame has spread far and wide that these gods appear before human kind and bring an unexpected aid to those among their initiates who call upon them in the midst of danger.

[5.49.6]
γίνεσθαι δέ φασι καὶ εὐσεβεστέρους καὶ δικαιοτέρους καὶ κατὰ πᾶν βελτίονας ἑαυτῶν τοὺς τῶν μυστηρίων κοινωνήσαντας. διὸ καὶ τῶν ἀρχαίων ἡρώων τε καὶ ἡμιθέων τοὺς ἐπιφανεστάτους πεφιλοτιμῆσθαι μεταλαβεῖν

τῆς τελετῆς· καὶ γὰρ Ἰάσονα καὶ Διοσκόρους, ἔτι δʼ Ἡρακλέα καὶ Ὀρφέα, μυηθέντας ἐπιτυχεῖν ἐν ἁπάσαις ταῖς στρατείαις διὰ τῆν τῶν θεῶν τούτων ἐπιφάνειαν.

[5.49.6] it is also said that those who have taken part in the mysteries become both more pious and more just and better in every respect than they were before. For this reason, we are told, the most celebrated of the ancient heroes and demi-gods eagerly desired to participate in the initiatory rite; indeed Jason, the Dioscuri, Heracles and Orpheus, after having been initiated succeeded in every undertaking they pursued, because these gods appeared before them.