John Wesley on Romans 2:15

Who show - To themselves, to other men, and, in a sense, to God himself. The work of the law - The substance, though not the letter, of it. Written on their hearts - By the same hand which wrote the commandments on the tables of stone. Their conscience - There is none of all its faculties which the soul has less in its power than this. Bearing witness - In a trial there are the plaintiff, the defendant, and the witnesses. Conscience and sin itself are witnesses against the heathens. Their thoughts sometimes excuse, sometimes condemn, them. Among themselves - Alternately, like plaintiff and defendant. Accusing or even defending them - The very manner of speaking shows that they have far more room to accuse than to defend.