That's a good observation. My preliminary response is that we read in Scripture that God created light by God's spoken word. Darkness is the nature (or condition) of the world without light. "Nature," in this sense does not equate with something created. Perhaps "characteristic" or "reality" might be good replacement for "nature" in this case. Similar to what we read throughout Scripture, I was intending to make a subtle distinction between the nature of the world versus the nature of God.