In a roughly 1600 year old sermon St. John Chrysostom discusses the passage from Romans 12:20 where the apostle Paul says “No, ‘if your enemy is hungry, feed him; if he is thirsty, give him drink; for by so doing you will heap burning coals upon his head.’”
Chrysostom notes the odd nature of the verse: it seems that Paul is encouraging people to do nice things for others out of a spirit of vengeance, which undermines the overall thrust of the context which tells the Roman Christians not to seek revenge but to overcome evil with good. There are a variety of ways that interpreters have tried to resolve this tension, and Chrysostom gives an interesting example of one such way:
“. . . That great and noble-minded man [Paul] was well aware of the fact that to be reconciled quickly with an enemy is a grievous and difficult thing; grievous and difficult, not on account of its own nature, but of our moral indolence. But he commanded us not only to be reconciled with our enemy, but also to feed him; which was far more grievous than the former. For if some are infuriated by the mere sight of those who have annoyed them, how would they be willing to feed them when they were hungry? And why do I speak of the sight infuriating them? If any one makes mention of the persons, and merely introduces their name in society, it revives the wound in our imagination, and increases the heat of passion. Paul then being aware of all these things and wishing to make what was hard and difficult of correction smooth and easy, and to persuade one who could not endure to see his enemy, to be ready to confer that benefit already mentioned upon him, added the words about coals of fire, in order that a man prompted by the hope of vengeance might hasten to do this service to one who had annoyed him. And just as the fisherman surrounding the hook on all sides with the bait presents it to the fishes in order that one of them hastening to its accustomed food may be captured by means of it and easily held fast: even so Paul also wishing to lead on the man who has been wronged to bestow a benefit on the man who has wronged him does not present to him the bare hook of spiritual wisdom, but having covered it as it were with a kind of bait, I mean the 'coals of fire,' invites the man who has been insulted, in the hope of inflicting punishment, to confer this benefit on the man who has annoyed him; but when he has come he holds him fast in future, and does not let him make off, the very nature of the deed attaching him to his enemy; and he all but says to him: 'if thou art not willing to feed the man who has wronged thee for piety’s sake: feed him at least from the hope of punishing him.' For he knows that if the man once sets his hand to the work of conferring this benefit, a starting-point is made and a way of reconciliation is opened for him. For certainly no one would have the heart to regard a man continually as his enemy to whom he has given meat and drink, even if he originally does this in the hope of vengeance. For time as it goes on relaxes the tension of his anger. As then the fisherman, if he presented the bare hook would never allure the fish, but when he has covered it gets it unawares into the mouth of the creature who comes up to it: so also Paul if he had not advanced the expectation of inflicting punishment would never have persuaded those who were wronged to undertake to benefit those who had annoyed them. Wishing then to persuade those who recoiled in disgust, and were paralysed by the very sight of their enemies, to confer the greatest benefits upon them, he made mention of the coals of fire, not with a view of thrusting the persons in question into inexorable punishment, but in order that when he had persuaded those who were wronged to benefit their enemies in the expectation of punishing them, he might afterwards in time persuade them to abandon their anger altogether.”
From John Chrysostom, "To those who had not attended the assembly," in NPNF; Grand Rapids: CCEL), 316-317.
In Chrysostom’s mind St. Paul is appealing to his audience’s baser motives in order to ‘trick’ them into doing something good, knowing that the good deed will actually transform those base motives, turning animosity into love. Regardless of whether or not you agree with Chrysostom’s exegesis, you have to admire both his creativity and his psychological insight. Well over a millennia before the rise of the modern social sciences this ancient preacher has beautifully captured a well-attested social psychological principle: our actions towards another person often change our attitudes towards them. If you don’t like someone, but you force yourself to say nice things to them or perform acts of service for them your attitudes towards them will actually be transformed – you will grow to like them. What's behind this is something psychologists call "cognitive dissonance." If our attitudes towards someone do not match up with our actions towards them it creates dissonance, and this dissonance can be resolved by changing our attitudes.
Where else might we see principles like these at work in ancient texts?
Additional Note: If you'd like a nice way to track down patristic quotations and allusions of biblical texts (like, for instance, if you wanted to find other early Christian writers who commented on Romans 12:20) be sure to check out Biblindex.