Origen is a remarkable figure. He was the student of Ammonius Saccas, the influential and mysterious Platonist that was also the teacher of Plotinus. He nearly offered himself as martyr in the persecution of 202 when his father was killed; his mother stopped him by hiding his clothes. His alternate name was "adimantios", which meant "man of steel". It is said that he underwent voluntary emasculation, to avoid sexual pleasure. He was extremely disciplined in both life and scholarship. Some say that he wrote 6000 volumes (papyrus roles), some say 2000. Relatively few are left. His discipline in scholarship extended to the organization of his work, not just the output. He always writes from a carefully thought-out perspective, even when he is just speculating.
Origen follows Plato in seeing the metaphysical realm as one in which the soul has descended from God, and must return. His structure differs from Plotinus, however, in that God is Being itself. This is like Augustine. He is anxious to maintain God's transcendence against the pagans who believed that God as participating equally in an essentially good cosmos, and God's accessibility against the Gnostics who pushed God to the extent of unknowability.
Origen picks up much of Plotinus' system, in which there are triads. God the Father is identified with Plotinus' One. Therefore, for Origen, God the Father is above being. Augustine, in contrast, makes God into being par excellance. The One then generates or gives rise to (he doesn't want to say "create") the Logos or Word, which is identified with Plotinus' Intelligence, and also with God the Son. The Word is or contains the exemplars (Platonic Forms) of all creatures, and physical creatures are made in the image of these. Then, there is the Holy Spirit, identified with Plotinus' Soul, below which are created and individual souls.
Note that there is a tendency to subordinate the Word and Holy Spirit to the Father on this scheme. This leads to a kind of Arianism. Furthermore, if we wanted to be thoroughly neo-Platonic, just as the Intelligence is identical with the intelligences (the Word is identical with its ideas, the Exemplars), so the souls should be identical with the Soul. This means that there is some pressure to see human souls as somehow divine. This is a result the influence of Greek thought on Christian theology before Nicaea. Origen fights this tendency by subordinating human souls to the Holy Spirit. He therefore departs from the straight Plotinian line.
Other features of Origen's doctrine:
1. Creation is necessary and eternal. This is heresy, from the point of view of later Christian theology. So, how does the relations between the persons of the Trinity differ from the relations between the God and creation? Strictly speaking, it cannot. Origen divides it up by saying that the first relationship is necessary, and the second is contingent. But this won't work. Either the second and third members of the Trinity are part of creation (Arianism), or creation is part of God (human souls are divine).
2. Creation is ex nihilo. This is decided on at Nicaea. Origen argues for it, by arguing that it is no more ridiculous than its opposite. You are going to have to deny the Principle of Sufficient Reason (to use an anachronistic term) somewhere, for if creation ex nihilo isn't true, you have to explain the eternal existence of matter.
3. Against Justin Martyr, Origen affirms the immateriality of human souls. This is a good neo-Platonic stance. Justin didn't want to do this because it would give human souls the mark of divinity. Origen didn't care about this.
4. All will be saved. There is no doctrine of hell. This is an echo of the Plotinian doctrine of the return of all things to the One.
5. Evil is a result of the soul's free will, not of matter. The soul pre-exists, and it is because of an evil choice on its part that it ends up in a body. The embodiment of souls is therefore a kind of Fall. So, the body is a prison, but is not evil.
6. God's power is finite. This is necessary so God can be perfect. The Greek notion of perfection requires definite limits. Indefiniteness is imperfection. Latin, too: perfectus just means "complete". So, if God's power is infinite, it would just mean we couldn't say what God could do.
7. The mystical ascent is made possible by Christ's work. This means that it is possible for any Christian, as opposed to the intellectual elite that are the mystics in Plato's and Plotinus' systems.