This cannot be before the soul is so joined to the body, that nothing may sever them. Yet it is rightly called the death of the soul, because it does not live of God; and the death of the body, because though man does not cease to feel, yet because this his feeling has neither pleasure nor health, but is a pain and a punishment, it is better named death than life.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: City of God, book xiii, ch. 2