Vigilance and Prayer

Ὥωπερ χρὴ τὸν ζῶντα διὰ παντὸς ἀναπνεῖν, οὕτω χρὴ διηνεκῶς ἐπιτηδεύειν καὶ μεταχειρίζεσθαι τὴν καλὴν ἀγρυπνίαν, καὶ μιμεῖσθαι τοῖς ψαλμοῖς καὶ τοῖς ὕμνοις τὸ τῆς μελιφθόγγου ἀηδόνος ἄγρυπνον, ἠνίκα ἂν ἐπυάζει δι' ὅλης νυκτὸς οὐκ ἀποπαυομένης τοῦ μελῳδειν. Τοῦτο γάρ σου ποιοῦντος, οὐκ ἁνέξεται ὁ ἐχθρὸς πολυχρονίως παρεδρεύειν σοι, ὁρῶν ἑαυτον ὑποθλιβόμενον τε καὶ ἐξουθενούμενον ὑπὸ σοῦ, καὶ τοῖς τῆς ἀγρύπνου εὐχῆς κεντητηρίοις καθεκάστην τιτρωσκόμενον νύκτα. Ἅγιος Νειλος, Βιβλιον Πρῶτον, Ἐπιστολὴ Λ' Τιμοθεῳ Ὑποδιακονῳ

Just as it is necessary to breath all the time one lives, so it is necessary to be vigilant and to turn to fair wakefulness and to be like the watchful nightingale of beautiful voice with Psalms and hymns that watching through the whole night there be no cessation of song. For doing this you will not be bitten by the enemy who at all times is near you, watching that he leap on you when you are negligent, and that in the interruption of vigilant prayer in the night he might strike wounds. Saint Nilus of Sinai, Book 1, Letter 30, To the Subdeacon Timotheus