We may have a suspicion that separation of the soul from the body is not per accidens but is in accord with nature. For man’s body is made up of contrary elements. Everything of this sort is naturally corruptible. Therefore the human body is naturally corruptible. But when the body corrupts the soul must survive as a separate entity if the soul is immortal, as in fact it is. Apparently, then, separation of the soul from the body is in accord with nature.
In view of these considerations, we must take up the question, how this separation is according to nature, and how it is opposed to nature. We showed above that the rational soul exceeds the capacity of all corporeal matter in a measure impossible to other forms. This is demonstrated by its intellectual activity, which it exercises without the body. To the end that corporeal matter might be fittingly adapted to the soul, there had to be added to the body some disposition that would make it suitable matter for such a form. And in the same way that this form itself receives existence from God alone through creation, that disposition, transcending as it does corporeal nature, was conferred on the human body by God alone, for the purpose of preserving the body itself in a state of incorruption, so that it might match the soul’s perpetual existence. This disposition remained in man’s body as long as man’s soul cleaved to God.
But when man’s soul turned from God by sin, the human body deservedly lost that supernatural disposition whereby it was unrebelliously subservient to the soul. And hence man incurred the necessity of dying.
Accordingly, if we regard the nature of the body, death is natural. But if we regard the nature of the soul and the disposition with which the human body was supernaturally endowed in the beginning for the sake of the soul, death is per accidens and contrary to nature, inasmuch as union with the body is natural for the soul.
St. Thomas Aquinas. (1265-1274). Compendium Theologiae: Separation of the Body from the Soul Both Natural and Contrary to Nature, trans. by Cyril Vollert. St. Louis & London: B. Herder Book Co., 1947
All scripture is given by inspiration of God and is profitable for doctrine, reproof, correction, and instruction in righteousness (2 Timothy 3:16).