From a conversation with the elder Archpriest Valerian Krechetov.
When a person learns to think, reason and at the same time prays, relies on God, checks his feelings, thoughts and intentions with the commandments - this is the process of purifying his heart. This is a very big job. Here Abba Dorotheus said: "I do not know of any other fall for a monk, except when he believes his heart." Yes - until it is purified. And it also seems to me that this is said in the sense that one must always keep such a thought - but maybe I am wrong. Allow such a possibility, recognizing the limitations of any private opinion. "Don't be too right" - there is such a saying. If Sisoes the Great, dying, said: "I do not know whether I have begun repentance," it means that he did not trust his heart to the end in this regard. Man is mistaken. Apostle Peter confessed Jesus Christ as the Son of God, but when Christ said that He must die on the cross, he retorted: “…May this not happen to You!” (Matthew 16:22).