We have to take particular care to follow the Gospel precept that bids us go into our inner room and shut the door to pray to our Father.
This is how to do it.
We are praying in our inner room when we withdraw our heart completely from the clamor of our thoughts and preoccupations, and in a kind of secret dialogue, as between intimate friends, we lay bare our desires before the Lord.
We are praying with our door shut when, without opening our mouth we call on the One who takes no account of words but considers the heart.
We are praying in secret when we speak to God with the heart alone and with concentration of the soul, and make known our state of mind to him alone, in such a way that even the enemy powers themselves cannot guess their nature. Such is the reason for the deep silence that it behooves us to keep in prayer…
Thus our prayers should be frequent but short, for fear that if they are prolonged the enemy might have an opportunity to insinuate distraction into them. This is true sacrifice: ‘A broken and a contrite heart, O God, thou wilt not despise’ (Psalm 51.17).
JOHN CASSIAN Conferences IX, 35-6