As for Paul and his times, the custom of smelters, metal workers, was to heap coals not only below the metal, but upon it as well, and thus melt it. Refine me, O Lord. This enemy, then – what are we to do with him? We wash his feet, certainly the custom. And we place cosseted coals on his head, also perhaps the custom. Of course the language is symbolic – the opportunity does not always arise to do these things, and so the specifics are generalized. Shall Paul's "heaping" of coals be likened to the "good measure, pressed down, and shaken together, and running over," that Jesus talks about? (Lk 6:38) Yes, as the context proves: "Be ye therefore merciful, as your Father also is merciful." (v. 36) But this in no way mitigates against the pain involved in Paul's imagery, contrasted with that of Jesus. The point, in Romans, is not hospitality, but transformation. Either we make a friend of an enemy, melt his recalcitrant heart, refine his enmity into amity, as Saul with David – or his iniquity will be confirmed, as was the hardness of the heart of Pharaoh … his malice will be the more inexcusable, his condemnation aggravated.
So what. I can make a case for my point? Bully for me. But the thing is, we are not told that God is Justice. We are not told that God is Mercy, nor Grace. What is it, that God is? There is a virtue that is specifically, and uniquely, Christian. Every faith that's not just some weird minor cult acknowledges and lauds the idea of love. But only one faith has identified God as Love. And it is in this, more than in any other thing, that we are to be perfect, even as our Father in Heaven is perfect.
Today, you see, I felt love, mildly. I saw, you see, a father with his little child. I jokingly said I was jealous. I wasn't, but it did bring home to me how much I miss that role. It also melted my hard heart, and reminded me of some important and neglected things. For some inexplicable reason I found myself opened up, slightly, wide enough to feel some small tenderness for the people around me. That's not so common nowadays, with me, for some inexplicable reason. I'm not a stranger to it. It just ends up being so painful. Look what it did to Jesus.