Gregory the Great — on 2Sam 12:1-6 (The Book of Pastoral Rule, Part 3, Chapter 2)

“But sometimes, when the powerful of this world are taken to task, they are first to be searched by certain similitudes, as on a matter not concerning them; and, when they have pronounced a right sentence as against another man, then in fitting ways they are to be smitten with regard to their own guilt; so that the mind puffed up with temporal power may in no wise lift itself up against the reprover, having by its own judgment trodden on the neck of pride, and may not try to defend itself, being bound by the sentence of its own mouth. For hence it was that Nathan the prophet, having come to take the king to task, asked his judgment as if concerning the cause of a poor man against a rich one, that the king might first pronounce sentence, and afterwards hear of his own guilt, to the end that he might by no means contradict the righteous doom that he had uttered against himself. Thus the holy man, considering both the sinner and the king, studied in a wonderful order first to bind the daring culprit by confession, and afterwards to cut him to the heart by rebuke. He concealed for a while whom he aimed at, but smote him suddenly when he had him. For the blow would perchance have fallen with less force had he purposed to smite the sin openly from the beginning of his discourse; but by first introducing the similitude he sharpened the rebuke which he concealed. He had come as a physician to a sick man; he saw that the sore must be cut; but he doubted of the sick man's patience. Therefore he hid the medicinal steel under his robe, which he suddenly drew out and plunged into the sore, that the patient might feel the cutting blade before he saw it, lest, seeing it first, he should refuse to feel it.”