The beginning of Prelest is Slothfulness with Regard to the Prayer and the Divine Services

St Isaac of Syria, The Ascetical Homilies, Homily 2.

The beginning of mind derangement (when it becomes visible in the soul) is to be seen, first of all, in slothfulness with regard to the Divine services and prayer. For except the soul first fall away from these, she cannot be led in the way of error; but as soon as she is deprived of God’s help, she easily falls into the hands of her adversaries. And again, whenever the soul becomes heedless of the labours of virtue, she is inevitably drawn to what is opposed to them. A transition, from whichever side it occurs, is the beginning of what belongs to the opposite party. Practice the work of virtue in your soul and do not concern yourself with futile matters. Always lay bare your weakness before God, and you will never be put to the test by aliens when you are found alone, distant from your Helper.

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