I have been reading what St. Thomas has to say on resurrection and how the human body will be changed afterwards. St. Thomas talks about how all people, the damned and the saints alike, will become immortals. He says the soul will communicate its natural immortality to the body.
Summa Contra Gentiles, CHAPTER LXXXIX--Of the quality of Risen Bodies in the Lost:
Now the human body, after the resurrection, will not be transmutable from form to form, either in the good or in the wicked; because in both it will be entirely perfected by the soul in respect of its natural being.
Summa Contra Gentiles, CHAPTER LXXXVI--Of the Qualities of Glorified Bodies:
The bodies of all men alike will be organised as befits the soul, so that the soul shall be an imperishable form giving imperishable being to the body, because to this effect the power of God will entirely subject the matter of the human body to the human soul.
Summa Theologiae, (This is from my notes and I forgot where exactly in the Summa this is):
But in the final state, after the resurrection, the soul will, to a certain extent, communicate to the body what properly belongs to itself as a spirit; immortality to everyone; impassibility, glory, and power to the good, whose bodies will be called "spiritual."
If this is the case, then why can't the soul keep the body from corruption now so that humans become naturally immortal without the need of any preternatural gift to keep us immortals?
I wish to get an answer from a metaphysical and Catholic perspective.