When one has attained the level of good thoughts, one should take extreme care to keep these points in mind, lest out of negligence or conceit one is deprived of God’s grace, as St Isaac says:
When God-given thoughts increase in a man’s soul and lead him toward greater humility and compunction, he should always give thanks, acknowledging that only by God’s grace does he know such things, and regarding himself as unworthy of them.
If good thoughts cease and his mind is once more darkened, losing its awe and its sense of inward grief, he should be greatly distressed and humble himself in word and deed; for grace has already abandoned him, so that he may realize his own weakness, acquire humility and try to amend his life, as St Basil the Great says: For had he not neglected that inward grief which is so dear to God he would not have lacked tears when he wished for them. That is why we should always be conscious of our own weakness and the power of God’s grace, and should neither lose hope if something happens to us, nor be emboldened to think that we are anything whatsoever. Rather we should always hope in God with humility.
St Peter of Damaskos Book, Philokalia V3.121