What is required of the repentant person when he falls into the same sin again?

St. Basil the Great answers, “He who has offended once and incurs this same sin again is seen to indicate this about himself: first that he is not purified of what is prior to the sin, from which, as from a kind of noxious root there sprout the same ills as before. It is as if someone cuts off the branches of a tree but leaves behind the root. As long as the root remains in the ground it will eventually generate shoots from the same stock. So also with sin: since not all who commit an offence take their impulse from the sins themselves—rather the cause of the offence arises from yet other offences—it is therefore necessary for him who wishes to purify himself wholly from sin to cut out from below the very first causes of defect. For example, if there has been something of strife and envy (cf. Rom 13:13, et al.), it does not take a beginning from itself, but has a root of arrogance and the love of human glory; for he who seeks glory from men either harries with disputes or envies those who act uprightly, that is, with anyone through whom he appears to be held in less praise or admiration.”¹⁴⁵⁸