Law And Spirit

Ὄν τρόπον τὰ τοῦ νόμου προοίμια φόβου ἐδεῖτο, πρὸς φυλακὴν τῶν ἐντολῶν ἐπιστρέφοντος τοὺς ἀκούοντας, καὶ ἐκ μέσου τοῦ πυρὸς ὁ Θεὸς ἐχρημάτιζεν· οὕτω καὶ μετὰ τὴν τοῦ Δεσπότου καὶ Σωτῆρος ἡμῶν ἀνάστασιν, ἐν πυρὶ τὸ Πνεῦμα τὸ ἅγιον τοῖς ἀποστόλοις ἑδιδοτο, βιαίας πνοῆς προηγουμένης, ἵνα εἰς Θεὸς ἐν ἀμφοτέραις ταῖς Διαθήκαις γνωσθῇ, εἰ καὶ πολὺ τῆς δευτέρας τὸ πρὸς τὴν προτέραν διάφορον. Ἡ μὲν γὰρ τυπικοῖς ἐχρῆτο προστάγμασιν, ἡ δὲ τοῖς ἀληθέσιν ἔλαμψε πράγμασί τε καὶ δόγμασινι. Ἅγιος Ἰσίδωρος Του Πηλουσιώτου, Βιβλίον Πρῶτον, Ἐπιστολή ΥϟΔ' Τιμοθεῳ Ἀναγνωστῃ Source: Migne PG 78.452a

As the first law required fear that the hearers would turn to the keeping of the commandments, and from the midst of fire God spoke his oracles, so after the resurrection of our Lord and Saviour, the Holy Spirit was given as a fire, with a strong wind coming before it, that the one God in the two Testaments be recognised, even if there is great difference between what came first and what came after. For the former made use of the commandments of types, and the latter blazed forth with true deeds and teachings. Saint Isidore of Pelusium, Book 1, Letter 494, To Timothy the Lector