4 So unbridled is their madness, that they declare they have in their power all things which are irreligious and impious, and are at liberty to practise them; for they maintain that things are evil or good, simply in virtue of human opinion. They deem it necessary, therefore, that by means of transmigration from body to body, souls should have experience of every kind of life as well as every kind of action (unless, indeed, by a single incarnation, one may be able to prevent any need for others, by once for all, and with equal completeness, doing all those things which we dare not either speak or hear of, nay, which we must not even conceive in our thoughts, nor think credible, if any such thing is mooted among those persons who are our fellow citizens), in order that, as their writings express it, their souls, having made trial of every kind of life, may, at their departure, not be wanting in any particular.
It is necessary to insist upon this, lest, on account of some one thing being still wanting to their deliverance, they should be compelled once more to become incarnate. They affirm that for this reason Jesus spoke the following parable:— “Whilst you are with your adversary in the way, give all diligence, that you may be delivered from him, lest he give you up to the judge, and the judge surrender you to the officer, and he cast you into prison. Verily, I say unto you, you shall not go out thence until you pay the very last farthing.” They also declare the “adversary” is one of those angels who are in the world, whom they call the Devil, maintaining that he was formed for this purpose, that he might lead those souls which have perished from the world to the Supreme Ruler.
They describe him also as being chief among the makers of the world, and maintain that he delivers such souls [as have been mentioned] to another angel, who ministers to him, that he may shut them up in other bodies; for they declare that the body is “the prison.” Again, they interpret these expressions, “You shall not go out thence until you pay the very last farthing,” as meaning that no one can escape from the power of those angels who made the world, but that he must pass from body to body, until he has experience of every kind of action which can be practised in this world, and when nothing is longer wanting to him, then his liberated soul should soar upwards to that God who is above the angels, the makers of the world.
In this way also all souls are saved, whether their own which, guarding against all delay, participate in all sorts of actions during one incarnation, or those, again, who, by passing from body to body, are set free, on fulfilling and accomplishing what is requisite in every form of life into which they are sent, so that at length they shall no longer be [shut up] in the body.
Source: Adversus haereses (New Advent)