How do people know what pleases God?  The Jews said that they had been given God's law through Moses.  But what about people who lived before Moses like Noah, Abraham, Isaac and Jacob?  Paul explains that they and all the Gentiles - indeed everybody - have been given an inbuilt understanding of right and wrong. We call it our conscience (Acts 24:16).

Those who obey their invisible conscience demonstrate that they know something of God's law.  They know that they are accountable to somebody greater than themselves.  They may have no other written information about how to obey God, but choosing to act according to their conscience pleases Him.  Choosing to disobey the secret voice reveals their selfish rebellion against Him.  

However, nobody always makes the right choice, either to God's written law or to their invisible conscience.  And so God's judgement on the final day will not be an assessment of how much we know His written law, but how completely we have obeyed either the law or our conscience or both.  Ultimately, it is only in trusting Jesus Christ whose blood can cleanse our conscience (Hebrews 9:14) that we can have peace of heart and a quiet conscience.  Then we can live in hope and not in fear of the return of Jesus, our King and Judge.

Of course, as we disobey our conscience it gets distorted and no longer alerts us to the sinfulness of wrong desires. Some might therefore say that their conscience is clear, even though God's Word declares them to be in the wrong.  So relying on that inner voice alone is inadequate.  But God still knows what is right, even if we have de-tuned our conscience, so He will judge us righteously.  But there will be many whose conscience troubles them; they want to be free from the guilt of sin.  That is why we must keep on being bold to tell the gospel message: it is the answer to their unspoken prayer.