Maybe we know what God is: There is only one Spirit in the universe and we all make up that Spirit. We make up that Spirit when we are created and after we die. God, all creation together is God, all creation working together to create all things. If the majority of spirits want a certain thing to happen it will, because we have the power of thought. If we are Spirit now and we came form spirit and are connected to other Spirits, we are the same as other Spirits, we are all equal and the same in Spirit we are only different in our physical bodies, all of us together are the Spirit of God. God made us in his image.
We were all part of God in the beginning, so we must still be part of God when we are born in a physical body an we must go back to Gods Spirit when this physical body dies.
So what is the purpose of it all? All the people of the earth are of the same Spirit ( only one Spirit) and this Spirit is God the Creator. God is Spirit not a spirit. Think of your wife in Spirit, she is the exact same Spirit as you are, your neighbor is exactly the same Spirit as you, all the people are exactly the same Spirit as you and that Spirit is God. All of our Spirits make the Spirit of God, all living things are part of the spirit of God. The Spirit of God is the ocean and we are all a cup of water from the ocean. When our physical body dies we go back to the ocean.
What is our purpose as Spirits of God here on earth? What is the purpose of an oak tree? To grow from a tiny acorn and become a beautiful huge tree that gives shelter and food for mammals, shelter for humans, shelter for birds and rebuilds the soil. The oak tree has no choice in what it must do. It does not think about what it is to do, it just does it. It does what God created it to do. We do what God created us to do, although we may not know what that is.
Let your spirit shine brightly for the world to see. Maybe that is your purpose! Do what God created you to do. Be his temple here on earth, and you will be rewarded.