The Harmony Of The Testaments

Καινότητα δογμάτων, ὦ φιλότυς, οὐδεμίαν τῷ νόμῳ καὶ τοῖς προφήταις ὁ τοῦ Θεοῦ Υἱος ἐπεισήγαγεν, ἀλλὰ τοῖς πάλαι περὶ αὐτοῦ προφανθεῖσι τὸ πέρας ἐπέθηκε. Καὶ πάντως νουνεχῶς τὴν Παλαιὰν ἀναπτύσσων, πάντα τὰ τῆς Νέας ἐν αὐτῇ κηρυχθέντα εὑρήσεις. Τοῖς τοίνυν ἐπὶ τῷ νόμῳ ἐρηρεισμένοις, καὶ ξένην ὁδὸν τὴν εὐαγγελικὴν οἰομένοις, ἐκ τῶν τοῦ νόμου ῥημάτων, τῶν τῆς χάριτος δογμάτων τὴν ἀλήθειαν τρανοῖ. Καὶ ὀψονται οὕτως ἀμφοτέρων τῶν Διαθηκῶν ἐνδιὰθετον συμφωνίαν. Ἅγιος Ἰσίδωρος Του Πηλουσιώτου, Βιβλίον Πρῶτον, Ἐπιστολή ΡΖ' Τιμοθεῳ Ἀναγνωστῃ Source:  Migne PG 78.256a

There was no new teaching, my friend, the Son of God introduced into the Law and the Prophets but truly to those who once foretold Him he placed an end. And certainly if you with full attention soul peruse the Old Testament you shall find that it contains everything which is proclaimed in the New Testament. So, then, with the new way and novel Gospel teaching understood as resting upon the law, from the words of the law the truth of the grace of the teaching is declared. Thus perceive the harmony of both Testaments. Saint Isidore of Pelusium,  Book 1, Letter 106, To Timotheus the Lector