27 So then, if souls lose all their knowledge on being lettered with the body, they must experience something of such a nature that it makes them become blindly forgetful. For they cannot, without becoming subject to anything whatever, either lay aside their knowledge while they maintain their natural state, or without change in themselves pass into a different state. Nay, we rather think that what is one, immortal, simple, in whatever it may be, must always retain its own nature, and that it neither should nor could be subject to anything, if indeed it purposes to endure and abide within the limits of true immortality. For all suffering is a passage for death and destruction, a way leading to the grave, and bringing an end of life which may not be escaped from; and if souls are liable to it, and yield to its influence and assaults, they indeed have life given to them only for present use, not as a secured possession, although some come to other conclusions, and put faith in their own arguments with regard to so important a matter.
Source: Against the Heathen (New Advent)