Eckhart taught that in the ground of the soul, beyond its faculties, there is something uncreated, where God’s ground is the soul’s ground and the soul’s ground is God’s ground. There the Son is born in the soul. Tauler and the Rhineland mystics developed the idea.
Ground of the soul
In Meister Eckhart, the innermost depth of the soul where God’s ground and the soul’s ground are one.
Also: grunt, Seelengrund