God's Prima Materia

God created light and then operated on the Prima Materia.

3 And God said, “Let there be light,” and there was light. 4 God saw that the light was good, and he separated the light from the darkness. 5 God called the light “day,” and the darkness he called “night.” And there was evening, and there was morning—the first day.

6 And God said, “Let there be a vault between the waters to separate water from water.” 7 So God made the vault and separated the water under the vault from the water above it. And it was so. 8 God called the vault “sky.” And there was evening, and there was morning—the second day.

He created Light first so he can see the operations of his work.  Then from verse 6 onward is His operation on the Prima Materia.

And going back to the very beginning, we can see that the Prima Materia existed even before the creation of light.

Genesis 1

New International Version (NIV)

The Beginning
1 In the beginning God created the heavens and the earth. 2 Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters.

in the Story, Water has always been there. Thus Water is the All pervasive and eternal first substance.

Water - The First Matter/Prima Materia that God First Operated On.