This, at least, is how I read the doctrine of Protestants as well as of Catholics. The rule and measure of duty is not utility, nor expedience, nor the happiness of the greatest number, nor State convenience, nor fitness, order, and the pulchrum. Conscience is not a long-sighted selfishness, nor a desire to be consistent with oneself; but it is a messenger from Him, who, both in nature and in grace, speaks to us behind a veil, and teaches and rules us by His representatives. Conscience is the aboriginal Vicar of Christ, a prophet in its informations, a monarch in its peremptoriness, a priest in its blessings and anathemas, and, even though the eternal priesthood throughout the Church could cease to be, in it the sacerdotal principle would remain and would have a sway.
Thus, Blessed John Henry Newman in his famous “Letter to the Duke of Norfolk.” The quote captures his brilliance as an essayist, the phrase “a long-sighted selfishness” a masterpiece of communication and construction. But, it does something else: While Newman is keen to differentiate conscience from any kind of subjective whim, the quotes captures the liveliness of conscience and the unmistakable fact that conscience speaks, as it were, inside of our lives. Not in any abstract categorization can it be affirmed or denied.
Source: National Catholic Reporter