What if a person says, “my conscience is clear”?

St. Basil the Great answers, “A similar thing happens to physical sicknesses. There are many diseases that are not felt by those who have them, yet they trust the physician’s diagnosis more than their own feeling of sickness. So also, for spiritual sickness, namely, sin. If one is unaware of his sin but does not condemn himself, he ought to trust in those who can see his case clearer. This is explained by the holy Apostles who though they were very much attached to the Lord, when they heard the Lord telling them that, ‘one of you will betray Me’ (Matt. 26:21), they preferred to trust in His word and yielded to His declaration, saying: ‘Lord is it I?’ (Matt. 26:22). St. Peter teaches us, that even though he was zealous in his humility, he refused His Master, Lord and God’s ministry (in washing his feet) and so he heard the words: ‘If I do not wash you, you have no part with Me’ (John 13:8), and he was thus convinced of this truth and so said: ‘Lord, not my feet only, but also my hands and my head!’ (John 13:9).”