The truth and righteousness of the law is something that is written on everybody's hearts - people understand it and know by nature that the commandments are good. "the Gentiles, which have not the law, do by nature the things contained in the law... Which shew the work of the law written in their heart, their conscience also bearing witness... (Romans 2:14-15)".
So it's not about self-interest and earning a place in heaven, it's about doing the right thing simply because it is the right thing to do. Of course, even non-Christians know this, it is something imprinted in human nature.
Being a Christian is about admitting you have failed to meet these standards, and you can then bear more good fruit through your works by the regeneration that God works in you.
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