Question:
Answer:
According to St. Thomas Aquinas, the soul is the locus of and explanation for our personal identity that spans life, death, and the afterlife. Our human individuality is rooted in the being (esse) that the soul receives from God and is not dependent on matter. Aquinas writes:
It must be said that everything is individuated in the same way that it has esse. . . . Accordingly, just as the esse of the soul is from God as from an active principle, and in the body as to its matter, neither does the esse of the soul perish with the perishing of the body. So also, the individuation of the soul, even if it were to have a certain relationship to the body, does not perish at the perishing of the body [Disputed Questions on the Soul, art. 1, ad. 2].
To be sure, the body belongs to the identity of the human person. But the body receives its identity as this body from the being that the soul communicates to it. For example, my identity as Karlo subsists in the soul. But because my body is united to my soul, the body takes on my identity and thus becomes essential to who I am.
When I die, I will retain my individuality through the being of my soul. And when my soul receives a body again in the resurrection of the dead, my soul will communicate to that matter its individuality, and thus make that body my body.
It is true that my resurrected body will not have the same atoms that my body is made up of now. But it still will be my body, since it will be individuated by the same soul that makes me an individual now.
This is no different than my soul individuating different matter over the course of my life up to today. The atoms that make up my body today are different than the atoms that made up my body seven years ago. But yet it is still my body, and belongs to my identity as an individual human being.