Prayer is Useless without Fear and Trembling
"If you are disheartened, pray, as the Apostle says (cf. James 5:13). Pray with fear, trembling, effort, with inner watchfulness and vigilance. To pray in this manner is especially necessary because the enemies are so milignant. For it is just when they see us at prayer that they come and stand beside us, ready to attack, suggesting to our intellect the very things we should not think about when praying; in this way they try to take our intellect captive and ot make our prayer and supplication vain and useless. For prayer is truly vain and useless when not performed with fear and trembling, with inner watchfulness and vigilance. When someone approaches an earthly king, he entreats him with fear, trembling and attention; so much the more, then, we should stand and pray in this manner before God the Father, the Master of all, and before Christ the King of Kings. For it is He whom the whole spiritual host and the choir of angels serve with fear and glorify with trembling; and they sing in unceasing praise to Him, together with the Father who has no origin, and with the all-holy and coeternal Spirit, now and ever through all the ages. Amen. (Evagrios the Solitary, an excerpt from On Asceticism and Stillness in the Philokalia, Volume 1, p. 37).