Theories of what it means to be a person are not new in literature, philosophy, or theology.
I will try to put this in the simplest terms I can (with the proviso that all pithy comments like this are inadequate on their own):
The human person in medieval literature is mystical.
There are a thousand and one ways to cut this up and explore it, in a variety of genres, but the essence is here: what does it mean to be a person?
99% of the population in medieval Europe was Catholic. Not just nominally so, but through-and-through. It percolated through every dimension of human society, including writing.
Yes, there were dissenters, and arguments from within (as in all societies). But this was the starting point: the human person is mystical, because they have Divine origins.