Marilynne Robinson at the American Scholar:
The idea of conscience as we think of it is reflected in the Greek of the New Testament. It is to be found in Plato as self-awareness, a capacity for self-appraisal. In the Hebrew Bible, it is pervasively present by implication, an aspect of human experience that must be assumed to be reflected in the writing of Paul and others. In Genesis a pagan king can appeal to the Lord on the basis of the integrity of his heart and the innocence of his hands, and learn that God has honored his innocence and integrity by preventing him from sinning unintentionally. The king’s sense of himself, his concern to conform his conduct to the standard he brings to bear on it, which is a standard God acknowledges, is a kind of epitome of the concept of righteousness so central to the Hebrew Bible. That the king is a pagan, a Philistine, suggests that Torah regards moral conscience as universal, at least among those who respect and cultivate it in themselves.
Beyond the capacity to appraise one’s own actions and motives by a standard that seems, at least, to stand outside momentary impulse or longer-term self-interest and to tell against oneself, conscience is remarkably chimerical. An honor killing in one culture is an especially vicious crime in another. The effective imprisonment at forced labor of unwed mothers, or of young women deemed likely to stray, was practiced until a few decades ago in a Western country, Ireland, despite the many violations of human rights this entailed.