Letters of St. Macarius of Optina. Volume VI. Letter 109.
...We find it worth to offer a remark for consideration for you, mother: the honorable A. has come to your convent with a very good disposition and desire to “seek Jesus,” that is, to attain His love. This her expression often reached us. This thing is very good and virtuous, but it needs to have a solid foundation, for love is tempted by the enemy. Due to her ardor and purity of soul, she will soon see comforting and sweet feelings in herself - this will give hope to her in finding Jesus and His love. But this feeling is very dangerous and close to delusion: not yet having a struggle with passions, not knowing own weakness and not yet getting humbled, comforting feelings are not reliable. Although they come, but in order to be careful to get them and not to be under the delusion with them, but to consider herself unworthy of that... Thus, we suggest that you take care to warn her if she has any sweet feelings so that she does not rely on them and does not consider them to be great; they will leave her soon. Otherwise, being under the delusion and having accepted them at the wrong time, she will soon lose them; and when there is already time, he will not receive them, like a careless and stupid farmer who, when he saw growth, would consider it a fruit and pick it: he will never receive the fruit in this case. Many people suffered, going this way, and went astray; instead of humility, having too high opinion of themselves, they attained arrogance... Remind her that the love of God is tempted by the enemy: various passions will arise, and it is necessary to struggle with them, and whoever has humility and wisdom, will have relief in the struggle; but he who has a sense of grandeur about himself, or who reassures himself of comforting feelings, faces a tougher struggle, so that, learning his weakness, he would humble himself. But for them defeat is unbearable and leads to cowardice: and this is a sign of their pride. One must be afraid of the delusion, which is diverse: either, having seduced with imaginary holiness, it will blind one’s spiritual eyes, or, by a flash of joyful and comforting actions, having lost them, it will fall into various passions; and when you lead her in a moderate and constant way, engaging with her attentively, then something good can be developed out of her over time ... and she should reveal all her words, deeds, thoughts and actions to you, for whatsoever doth make manifest is light, and everything hidden is darkness (Eph. 5, 13)