Even Gentiles, who do not have God’s written law, show that they know his law when they instinctively obey it, even without having heard it. They demonstrate that God’s law is written in their hearts, for their own conscience and thoughts either accuse them or tell them they are doing right.
God’s law is written on the human heart from birth. We can see that in the way those that have never read the Bible, act rightly with conscience. The one puzzle piece missing from their lives is knowing the One who placed that desire there from the beginning.