Abba Irenaeus said to the brethren:
"Let us fight diligently and be patient in our warfare, for we are soldiers of the Heavenly King. And as the soldiers of an earthly king wear helmets, so we have heavenly graces - the beautiful virtues. They have breast-plates of chain-mail and we have the spiritual breast-plate forged with the bronze of faith. They have a spear; we have a cross. They have a shield; we have our hope in God. They have the oblong shield; we have God. In war they shed blood whereas we surrender our wills. That is why the Heavenly King conceded that the demons should do battle with us - that we not forget His benefits.
Many men, in their slackness, do not pray at all; or, if they pray, do not pray continuously but wander in their thoughts. They will be found to be no better than those who do not pray at all. For how shall they be heard who speak to God with their lips while they are reckoned to be of the world in their hearts? When we are afflicted, then we soberly give ourselves to prayer (for we often sing with our lips but not with our attention), sending up the eye our heart as we pray to God, speaking to Him with sighs.
So now, brothers, let us imitate the soldiers of the mortal king and fight with zeal, or rather the Three Children [Dan. 13] and tread down the furnace of passions by purity. Let us quench the coals of temptation by prayer. Let us put the imaginary Nebuchadnezzar (the devil) to shame, setting forth our bodies as a living sacrifice to God and offering a religious mind as a burnt sacrifice."
From The Spiritual Meadow of John Moschas, translated by John Wortley, Mioni 9.