“ Fiery coals ” is a reference to an ancient method of smelting ore by heating it from above and below to extract the metals.
عَلَى نَحْوٍ مُمَاثِلٍ ،‏ يُمْكِنُ لِلُّطْفِ أَنْ يُلَيِّنَ مَوْقِفَ ٱلْأَشْخَاصِ ٱلْغَضُوبِينَ وَيُبْرِزَ مَا فِيهِمْ مِنْ صِفَاتٍ حَسَنَةٍ .‏