From the writings of the Rev. Billy Graham
Dear Dr. Graham:
Since the soul cannot be seen, how can we know it is real? And the same is true of the conscience; it cannot be seen so is it a figment of imagination or the voice of God’s Spirit?
Dear C.D.: “And the Lord God formed man ... and man became a living soul” (Genesis 2:7, KJV). Likewise, “(the) conscience also (bears) witness” (Romans 2:15).
God has put within each one of us something that cries aloud against us; it bears witness whenever we do that which we know to be wrong (Romans 1:19, 2:15). The conscience is the detective that watches the direction of our steps and decries every conscious transgression. It is not imagination but rather a vigilant eye before which each imagination, thought and act, is held up for either censure or approval.
Every human being is a living soul with a conscience (described as the light of the soul, Proverbs 20:27), not to be confused with the Holy Spirit which resides only in those who belong to God through salvation in His Son Jesus Christ.
The conscience causes a warning light to go on inside when we do wrong. It wants to steer us away from evil and toward good. Even when the conscience is dulled or darkened by sin, it can still bear witness to the reality of good and evil, and to the holiness of God.
The German philosopher, Immanuel Kant, once stated that there were two things that filled him with awe — the starry heavens above and the human conscience within.
Persistent sin can dull or even silence our conscience. On the other hand, persistent attention to God’s Word will sharpen our conscience and make us more sensitive to moral and spiritual danger. We are instructed to “cleanse our conscience” (Hebrews 9:14), “not with fleshly wisdom but by the grace of God” (2 Corinthians 1:12).