Copied from an encyclopedia article, which is more eloquent than I am:
Origen did not believe in the eternal suffering of sinners in hell. For him, all souls, including the devil himself, will eventually achieve salvation, even if it takes innumerable ages to do so; for Origen believed that God’s love is so powerful as to soften even the hardest heart, and that the human intellect – being the image of God – will never freely choose oblivion over proximity to God, the font of Wisdom Himself. Certain critics of Origen have claimed that this teaching undermines his otherwise firm insistence on free will, for, these critics argue, the souls must maintin the freedom to ultimately reject or accept God, or else free will becomes a mere illusion. What escapes these critics is the fact that Origen’s conception of free will is not our own; he considered freedom in the Platonic sense of the ability to choose the good. Since evil is not the polar opposite of good, but rather simply the absence of good – and thus having no real existence – then to ‘choose’ evil is not to make a conscious decision, but to act in ignorance of the measure of all rational decision, i.e., the good. Origen was unable to conceive of a God who would create souls that were capable of dissolving into the oblivion of evil (non-being) for all eternity. Therefore, he reasoned that a single lifetime is not enough for a soul to achieve salvation, for certain souls require more education or ‘healing’ than others. So he developed his doctrine of multiple ages, in which souls would be re-born, to experience the educative powers of God once again, with a view to ultimate salvation. This doctrine, of course, implies some form of transmigration of souls or metempsychosis. Yet Origen’s version of metempsychosis was not the same as that of the Pythagoreans, for example, who taught that the basest of souls will eventually become incarnated as animals. For Origen, some sort of continuity between the present body, and the body in the age to come, was maintained (Jerome, Epistle to Avitus 7, quoting Origen; see also Commentary on Matthew 11.17). Origen did not, like many of his contemporaries, degrade the body to the status of an unwanted encrustation imprisoning the soul; for him, the body is a necessary principle of limitation, providing each soul with a unique identity. This is an important point for an understanding of Origen’s epistemology, which is based upon the idea that God educates each soul according to its inherent abilities, and that the abilities of each soul will determine the manner of its knowledge. We may say, then, that the uniqueness of the soul’s body is an image of its uniqueness of mind. This is the first inkling of the development of the concept of the person and personality in the history of Western thought.