If he could create a spirit as he wanted and Alessa gave her the body, essentially, this woman would belong to both. She was an entity of this spirit world. She had the body given to her by 'Her Mother', the Progenitor, and at the same time, the spirit given to her by 'Her Father', the Essence.
But.
The question that reigned in Matt's head was, 'Can I give her a different body to the spirits? Can I take these spirits to walk in my world and have a perfect connection with both worlds?'
Even more...
Spirits have a problem: Their abilities cannot develop in the spirit world more than what they already have from birth. There are ways to develop, but it involves falling into the dark practices of the world. Another way to develop is through contracts they form with humans or other races.
That also gives them greater potential for growth in their own world.