I'm not sure about that. What makes you think it is God's mind? Why couldn't it be, for example, the mind of John Malkovich?
It goes back to the meaning of the Logos. As in John 1:1, in the beginning was the Word. Logos is translated as Word. I take that as Mind, although there are other metaphors, the NT is jam packed with parables about this.
It is the thing behind consciousness, behind soul, behind personality, behind You.
John Malkovich also has a piece of the Mind.
We can explain biology and evolution and chemical processes, rightly or wrongly, but we can't explain consciousness. Where did that come from? We can't know that, it's a total mystery. So we'll just call it the Mind.