The words of Abbot Isaac on the nature of prayer.
The aim of every monk and the perfection of his heart tends to continual and unbroken perseverance in prayer, and, as far as it is allowed to human frailty, strives to acquire an immovable tranquillity of mind and a perpetual purity, for the sake of which we seek unweariedly and constantly to practise all bodily labours as well as contrition of spirit. And there is between these two a sort of reciprocal and inseparable union. For just as the crown of the building of all virtues is the perfection of prayer, so unless everything has been united and compacted by this as its crown, it cannot possibly continue strong and stable. For lasting and continual calmness in prayer, of which we are speaking, cannot be secured or consummated without them, so neither can those virtues which lay its foundations be fully gained without persistence in it. And so we shall not be able either to treat properly of the effect of prayer, or in a rapid discourse to penetrate to its main end, which is acquired by labouring at all virtues, unless first all those things which for its sake must be either rejected or secured, are singly enumerated and discussed, and, as the Parable in the gospel teaches, whatever concerns the building of that spiritual and most lofty tower, is reckoned up and carefully considered beforehand. But yet these things when prepared will be of no use nor allow the lofty height of perfection to be properly placed upon them unless a clearance of all faults be first undertaken, and the decayed and dead rubbish of the passions be dug up, and the strong foundations of simplicity and humility be laid on the solid and (so to speak) living soil of our breast, or rather on that rock of the gospel, and by being built in this way this tower of spiritual virtues will rise, and be able to stand unmoved, and be raised to the utmost heights of heaven in full assurance of its, stability. For if it rests on such foundations, then though heavy storms of passions break over it, though mighty torrents of persecutions beat against it like a battering ram, though a furious tempest of spiritual foes dash against it and attack it, yet not only will no ruin overtake it, but the onslaught will not injure it even in the slightest degree.
SAINT JOHN CASSIAN'S CONFERENCES, THE FIRST CONFERENCE OF ABBOT ISAAC ON PRAYER,NICENE AND POST-NICENE FATHERS, SERIES II VOLUME XI