Jeremiah 2:35

(Ver. 35, 36) And you said: I am without sin and innocent: and therefore let your anger turn away from me. Behold, I will contend with you in judgment, because you have said: I have not sinned: how despicable you have become, repeating your ways too much (or how greatly you have despised). This should be used against those who refuse to acknowledge their own sins: but in the time of affliction and distress, they claim to unjustly endure what they endure: and they provoke the wrath of God even more, because the greater sin is not to mourn what they have done, but to offer empty excuses for their sins. He said, 'I will argue with you in court for what you have said, 'I have not sinned': as if this sin is any greater, to have something in one's conscience and to speak it out in one's words. Let the new heresy hear that the wrath of God is even the greatest, not to humbly confess one's sin, but shamelessly boast of righteousness.'

It makes God angry for us to imagine that we are free from all impurity. He is even found saying to one of those who led polluted lives, Behold, I have a suit with you because you say I have not sinned, in that you have acted very contemptuously in repeating your ways. For the repetition of the way to sins is for us, when we are overtaken by offenses, to refuse to believe that we are guilty of the defilement that arises from them.

Let us, therefore, pray without ceasing, according to the expression of the blessed Paul. Let us be careful to do so aright.… Remember him who says by the voice of Isaiah, Declare your sins first, that you may be justified; remember too that he rebukes those who will not do so and says, Behold, I have a judgment against you, because you say I have not sinned. Examine the words of the saints, for one says, "The righteous is the accuser of himself in the beginning of his words," and another says, "I said, I will confess against myself my transgression to the Lord; and you forgave the iniquity of my heart."

For God readily accepts and has mercy on those who do not forget their offenses but fall down before him and ask of him forgiveness. But he is severe, and very justly so, on the hardhearted and the proud, and on one who in his great ignorance acquits himself of blame. For God said to one thus disposed, Behold, I have a suit against you, because you say, I have not sinned. For who can boast that he has a pure heart? Or who can have confidence that he is undefiled by sins? The road then to salvation, and which delivers those who earnestly walk on it from the wrath of God, is the confession of offenses, and to say in our prayers to him who purifies the wicked, Forgive us our sins.