Athanasius employs much of the same language and makes some of the same conceptual moves in talking about the Son’s relation to the Father on the one hand and the Son’s incarnation in the flesh on the other.

The Son is “proper to” the Father’s essence; so too the flesh of the Son to the Son.  The Son is the Father’s very own Word and Wisdom; so too the Son’s flesh is His very own.  The Son is not “alien” or “external” to the Father; so the Son’s flesh and its passions are not “external” to the Son.  In turn, believers become “proper” to the Son, sharing a new, heavenly nature and origin, participating in the immortality of the Son.

Crucially, of course, the Son’s flesh is acquired, not inherent; our union with the Son is not by nature.  There is an intrinsicism of nature (Father-Son) and one of grace.  The line between nature and grace is the very same as the line between Creator and creature.

Distinct though they are, the two intrinsicisms are, if you’ll pardon, intrinsic to one another.  We don’t become “proper” to the Son unless the Son’s flesh is “proper” to Him, and unless the Son is “proper” to the Father.