For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves: Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another;) In the day when God shall judge the secrets of men by Jesus Christ according to my gospel.

Romans 2:14-17 - KJV

 

(Indeed, when Gentiles, who do not have the law, do by nature things required by the law, they are a law for themselves, even though they do not have the law, since they show that the requirements of the law are written on their hearts, their consciences also bearing witness, and their thoughts now accusing, now even defending them.) This will take place on the day when God will judge men's secrets through Jesus Christ, as my gospel declares.

Romans 2:14-17 - NIV

For when Gentiles who do not have the Law do instinctively the things of the Law, these, not having the Law, are a law to themselves, in that they show the work of the Law written in their hearts, their conscience bearing witness, and their thoughts alternately accusing or else defending them, on the day when, according to my gospel, God will judge the secrets of men through Christ Jesus.

Romans 2:14-17 - NASB

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Here is an Indian’s humorous, though very significant definition of conscience. This is from It is Hard to Be a Christian, by Samuel M. Zwemer.

"It is a little three-cornered thing inside of me. When I do wrong it turns around and hurts me very much. But if I keep on doing wrong, it will turn so much that the corners become worn off and it does not hurt me any more."

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There is a difference between him who does no misdeeds because of his own conscience and him who is kept from wrong-doing because of the presence of others.

The Talmud