The nature of God is what makes God, God, and it is a nature that only he can have. That is, "God is a spirit, infinite, eternal, and unchangeable, in his being, wisdom, power, holiness, justice, goodness, and truth."
https://www.ligonier.org/guides/the-nature-of-god
It is like the translation of John 1:1c--"and the Word was God." It is a qualitative statement that could be translated as "and the Word was in nature God," however, since only God can have the nature of God, it is to essentially say the same thing as "and the Word was God."