Melito of Sardis, Fragment on the Incarnation
There is no necessity for those who have understanding to prove the true and invisible reality of His soul and body, the human nature as we know it, from what Christ did after His baptism. For the works Christ performed after the baptism, and especially the signs, revealed His deity concealed in flesh and convinced the world. For being God and at the same time also perfect man, He Himself guaranteed to us His two substances: the one indeed His deity through the signs during the three years after the baptism, and the other His humanity during the thirty years before the baptism, in which, because of the imperfection of the flesh, He was hiding the signs of His deity, even though He was true God existing before the ages.
Greek
Οὐδεμία ἀνάγκη τοῖς νοῦν ἔχουσιν, ἐξ ὧν μετὰ τὸ βάπτισμα ὁ Χριστὸς ἔπραξε, παριστᾶν τὸ ἀληθὲς καὶ ἀφανταστὸν τῆς ψυχῆς αὐτοῦ καὶ τοῦ σώματος, τῆς καθ' ἡμᾶς ἀνθρωπίνης φύσεως. Τὰ γὰρ μετὰ τὸ βάπτισμα ὑπὸ Χριστοῦ πραχθέντα, καὶ μάλιστα τὰ σημεῖα, τὴν αὐτοῦ κεκρυμμένην ἐν σαρκὶ θεότητα ἐδήλουν, καὶ ἐπιστοῦντο τῷ κόσμῳ. Θεὸς γὰρ ὢν ὁμοῦ τε καὶ ἄνθρωπος τέλειος ὁ αὐτὸς τὰς δύο αὐτοῦ οὐσίας ἐπιστώσατο ἡμῖν, τὴν μὲν θεότητα αὐτοῦ διὰ τῶν σημείων ἐν τῇ τριετίᾳ τῇ μετὰ τὸ βάπτισμα, τὴν δὲ ἀνθρωπότητα αὐτοῦ ἐν τοῖς τριάκοντα χρόνοις τοῖς πρὸ τοῦ βαπτίσματος, ἐν οἷς διὰ τὸ ἀτελὲς τὸ κατὰ σάρκα ἀπέκρυβε τὰ σημεῖα τῆς αὐτοῦ θεότητος, καίπερ θεὸς ἀληθὴς προαιώνιος ὑπάρχων.