11 But if concerning us men you will have other examples also set before you, come on to the blessed David, and take him for an example of repentance. Great as he was, he fell: after his sleep, walking in the eventide on the housetop, he cast a careless look, and felt a human passion. His sin was completed, but there died not with it his candour concerning the confession of his fault. Nathan the Prophet came, a swift accuser, and a healer of the wound. The Lord is angry, he says, and you have sinned. So spoke the subject to the reigning king.
But David the king was not indignant, for he regarded not the speaker, but God who had sent him. He was not puffed up by the array of soldiers standing round: for he had seen in thought the angel-host of the Lord, and he trembled as seeing Him who is invisible; and to the messenger, or rather by him in answer to God who sent him, he said, I have sinned against the Lord. Do you see the humility of the king? Do you see his confession? For had he been convicted by any one?
Were many privy to the matter? The deed was quickly done, and straightway the Prophet appeared as accuser, and the offender confesses the fault. And because he candidly confessed, he received a most speedy cure. For Nathan the Prophet who had uttered the threat, said immediately, The Lord also has put away your sin. You see the swift relenting of a merciful God. He says, however, You have greatly provoked the enemies of the Lord. Though you had many enemies because of your righteousness, your self-control protected you; but now that you have surrendered your strongest armour, your enemies are risen up, and stand ready against you.
Source: Catechetical Lectures (New Advent)