Conscience is not a reliable guide because it functions only according to what it has been taught and how it has been exercised, not according to any standard installed at birth. A person ignorant of God's standards can do evil with a perfectly clear conscience, as John 16:2 shows in those who kill believers and think they serve God. Conscience also adjusts in the direction it is exercised: repeated sin dulls remorse until a person is hardened, inured to sin, and finally "past feeling" (Ephesians 4:19), as Hebrews 3 warns even of Christians who merely drift through neglect. Because everyone is formed by a world God likens to a drunk, whose judgments cannot be trusted, natural feelings about right and wrong must be reviewed and changed. Job considered himself upright by the standards of his culture, yet before God he was staggering in unaware drunkenness, and he came to abhor himself. Sincerity does not make an act righteous; a lie told in ignorance still misleads and misses the mark. Following conscience preserves integrity, but an act is righteous only if it agrees with what God would do. Even the strong in Romans 14, theologically correct and acting on conviction, sinned by offending a weaker brother. Conversion re-educates the conscience toward God's righteousness and makes it increasingly sensitive.

Conscience is not a reliable guide because it does not determine right and wrong; it only recognizes and responds to whatever standards a person has been educated in. Scripture shows no set of values installed by God at birth, as the diversity of cultures and moral opinions demonstrates, and Jeremiah 10:23 says man's way is not in himself. Conscience therefore adapts to its environment, and since human nature tends downward, it slides when a culture or false doctrine drops God's standards. Paul persecuted Christians "in all good conscience" (Acts 23:1) because his education was incomplete, and Jesus warned that people would kill His followers thinking they served God (John 16:2). Titus 1:15 shows a conscience can be defiled, and Romans 1 shows that when God is left out, the heart darkens and the mind becomes reprobate. Ephesians 4:19 describes people "past feeling" who do evil with a clear conscience. Repeated sin hardens conscience step by step, from horror to regret, rationalization, and indifference, much like addiction. Feelings also mislead, since satisfied desire feels sweet even when evil (Proverbs 13:19), so the thinking mind, educated in God's way, must sometimes override feeling. One should live according to conscience but not fully trust it. Conversion and growth in the knowledge of Christ gradually educate it upward toward God's standards.