Against Heresies: Book II
Chapter 33: The Illogical Theory of Reincarnation
We can challenge their belief in transmigration from body to body with the fact that souls remember nothing of the events from their previous states of existence. If souls were sent for the purpose of experiencing every kind of action, they must necessarily remember past actions to complete the areas they lack. Otherwise, they would continue endlessly pursuing the same endeavors in vain. The combination of a body with a soul could not completely erase the memory and reflection of past experiences, especially since the purpose of entering the world was for this reason. Just as, when the body is asleep and at rest, the soul sees and does things in a vision and remembers them, it shares them with the body. Upon waking up, even after a long time, one can recount what was seen in a dream. Similarly, one would certainly remember the actions taken before entering this particular body. If what is seen for a short period or conceived briefly in a dream is remembered after the soul has rejoined the body and spread throughout its members, then it is even more likely it would remember experiences from a long-previous life.
Regarding these objections, Plato, the ancient Athenian who was the first to introduce this idea, when he couldn't dismiss them, invented the concept of a cup of oblivion, thinking that this would solve the issue. He offered no proof for his theory but simply asserted, without evidence, that when souls enter this life, they are made to drink from the cup of oblivion by the demon who oversees their entry into the world, before they enter their assigned bodies. He overlooked that in saying this, he created an even greater problem. For if the cup of oblivion, once drunk, can erase the memory of all past deeds, how, O Plato, do you claim knowledge of this (since your soul is now in the body), that before entering the body, it was made to drink by the demon a potion causing oblivion? For if you remember the demon, the cup, and the entry into life, you should also know about other matters; but if you don't, then the story of the demon and the cup of oblivion is false.
In response to those who claim that the body itself is the cause of forgetfulness, consider this: How is it, then, that whatever the soul perceives through its own means, whether in dreams or through deep reflection while the body is inactive, it remembers and shares with others? If the body were indeed the cause of forgetfulness, then the soul, while within the body, would be unable to remember things perceived long ago through the eyes or ears. As soon as one looked away from something, the memory of it would surely be lost. For the soul, existing in what they say is the very cause of forgetfulness, could know only what it saw right at that moment. How, then, could it learn of divine things and remember them while in the body, if the body were truly the cause of forgetfulness? However, the prophets also, when they were on earth, remembered and recounted to others whatever they saw or heard spiritually in visions of heavenly matters after returning to their normal mindset. Thus, the body does not cause the soul to forget those spiritually witnessed things; rather, the soul guides the body and shares with it the spiritual vision it has experienced.
The body does not have more power than the soul, as the body is given life, energy, growth, and cohesion by the soul; but the soul controls and governs the body. It is undoubtedly slowed down in speed to the extent that the body participates in its movement; yet it never loses the knowledge that belongs to it. The body can be seen as an instrument, while the soul embodies the reasoning of an artist. Just as an artist quickly forms an idea in their mind but can only execute it gradually with an instrument due to the lack of perfect flexibility in the material, thus blending the quickness of their mental process with the slow action of the instrument results in a moderate progress towards their goal. Similarly, the soul, when united with its body, is somewhat hindered, mixing its swiftness with the body's slowness. Yet, it does not completely lose its unique powers; while sharing life with the body, it continues to live. In doing so, while imparting other things to the body, it retains both the knowledge and memory of things it has observed.
If, therefore, the soul remembers nothing from a previous existence but perceives the things here, it follows that it never existed in other bodies or experienced things it cannot now recall or contemplate. Just as each of us receives a body through the skillful work of God, we also receive our soul. For God is not so lacking in resources that He cannot grant each individual body its proper soul, just as He gives it its specific character. Therefore, when the predetermined number is reached, all those who have been chosen for eternal life will rise again with their own bodies, souls, and spirits, in which they pleased God. On the other hand, those deserving punishment will go into it, also with their own souls and bodies, in which they distanced themselves from God's grace. Both groups will cease to procreate and marry, so that the number of humanity, according to God's foreordained plan, being completed, may fully fulfill the Father's scheme.