His Nature

Hebrews 1:3 ESV 

He is the radiance of the glory of God and the exact imprint of his nature, and he upholds the universe by the word of his power. After making purification for sins, he sat down at the right hand of the Majesty on high,

Romans 2:14

For when Gentiles, who do not have the law, by nature do what the law requires, they are a law to themselves, even though they do not have the law.

The light of the world is the radiance of the glory of God and the exact imprint of His nature. This is the man Jesus. Those in Christ begin a transformation into the nature of Christ. His nature is what the law requires. We have to be in His body before He can enter ours. A natural man can then become the natural man God intended.