The confusion about God's law written on our hearts

In the Bible it is said that all people have God's law written on our heart. I.e. *all* - not just the born again.

Rom 15 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...

Yet it also says that once born again, or regenerated, the Spirit writes God's law on our heart:

16 This is the covenant that I will make with them after those days, saith the Lord, I will put my laws into their hearts, and in their minds will I write them;

If you search for an answer to this confusion you find that theologians are all over the board on it. Calvin answered it directly though. He said 'law' as Hebrews is using the word refers to grace and is meant in contrast to the Covenant of Works, or the law of works. He didn't go far enough in his explanation though.

The phrase needed to understand the difference is Law of Christ.

This question goes to the heart of the deep, foundational subject of law and gospel. The book to get understanding of it is that mysterious book titled the Marrow of Modern Divinity by Edward Fisher.

Yes, we are born with God's law written on our heart. This is so we have no excuse. We can't claim ignorance for our rebellion. But that law is a curse because we can't fulfill it, but once we are regenerated by the word and the Spirit that law (call it the Ten Commandments for shorthand) becomes the law of Christ. It's no longer a curse to us because Christ fulfilled it and paid the price of death in our place for the penalty of not fulfilling it. And the heart in us that it's written on is our new heart God gives us (which is probably why there is a double writing because there are two hearts involved, our old heart which gets replaced by our new heart).

Now we have an inclination to follow the law because it's of the nature of our new heart to follow the law. The law is not external rules but intrinsic attributes of our new heart. And the law is obviously no longer a curse or a threat.