Nicene and Post-Nicene Fathers, Ser. II, Vol. XI:
The Works of John Cassian.: Chapter XXXV. Of prayer to be offered within the chamber and with the door shut.

Chapter XXXV.

Of prayer to be offered within the chamber and with the door shut.

Before all things however we ought most carefully to observe the Evangelic precept, which tells us to enter into our chamber and shut the door and pray to our Father, which may be fulfilled by us as follows: We pray within our chamber, when removing our hearts inwardly from the din of all thoughts and anxieties, we disclose our prayers in secret and in closest intercourse to the Lord. We pray with closed doors when with closed lips and complete silence we pray to the searcher not of words but of hearts. We pray in secret when from the heart and fervent mind we disclose our petitions to God alone, so that no hostile powers are even able to discover the character of our petition. Wherefore we should pray in complete silence, not only to avoid distracting the brethren standing near by our whispers or louder utterances, and disturbing the thoughts of those who are praying, but also that the purport of our petition may be concealed from our enemies who are especially on the watch against us while we are praying. For so we shall fulfil this injunction: “Keep the doors of thy mouth from her who sleepeth in thy bosom.” 1658

Footnotes

Micah vii. 5.