Originally there was one great being, and nothing else. This being eventually became lonely, 'He' had no-one to communicate with, no-one to love and no-one to be loved by. Just like ours, His most basic need is companionship. This situation caused Him much loneliness and sadness.
This being is what we know of as 'God'. In His infinite wisdom He realised that He needed to create a companion for Himself. God is not flesh and bone, nor is he spirit, He exists on a mental plane, in a mind form. This does not mean He does not exist, nor does it mean He is imaginary. For this reason, being a 'mind ' form He created another 'mind' form - hence God created man in His own image.
He also realised that giving this created mind form a predetermined personality would be like cloning Himself which make the companion unsuitable for companionship. This companion had to learn and progress and develop its own individual personality just as a baby develops a personality of its own as it grows and experiences life and all it has to offer. God effectively had to send His new friend to 'school' and for this purpose He created the universes and planets. On certain of these planets He placed everything required for sustaining life and promoting progress. These planets were His classrooms and the Universe His 'Department of Education'.
The created mind form in the state it was would not have been able to learn, so He subdivided it into many groups - spirit groups and these were allowed to choose which 'school' they wished to attend. Some chose the planet Earth while many, many others distributed themselves throughout the universe choosing the 'school' that they felt most comfortable with. For now we will concentrate on those who chose the Earth as the progress of the others run roughly along the same line as ours.
When the mind form was subdivided into spirit groups and sent down to the created spirit world to live they had to be given spirit bodies in order to be able to exist in it. These spirit groups were subdidvided yet again in the spirit world into soul groups, and it is these soul groups that undertook the first incarnations on the physical Earth.
Once the lessons from this school have been learnt and the souls progress they move up through the levels of spirit until 'Heaven' is reached, there all the soul groups rejoin into the original spirit groups. From there they progress in the group form until 'Nirvana' is reached where they wait for all spirit groups to rejoin ready for the return to God.