English translation of Origen's De Principiis, Book I, Chapter 6.3, "On the End of Consummation" from Alexander Roberts and James Donaldson, eds., The Ante-Nicean Fathers Translations of the Fathers Down to A.D. 325, Vol, 4 (Grand Rapids, MI: Wm. B. Eerdmans Publishing Co., 1994).
It is to be borne in mind, however, that certain beings who fell away from that one beginning of which we have spoken, have sunk to such a depth of unworthiness and wickedness as to be deemed altogether undeserving of that training and instruction by which the human race, while in the flesh, are trained and instructed with the assistance of the heavenly powers; and continue, on the contrary, in a state of enmity and opposition to those who are receiving this instruction and teaching. And hence it is that the whole of this mortal life is full of struggles and trials, caused by the opposition and enmity of those who fell from a better condition without at all looking back, and who are called the devil and his angels, and the other orders of evil, which the apostle classed among the opposing powers. But whether any of these orders who act under the government of the devil, and obey his wicked commands, will in a future world be converted to righteousness because of their possessing the faculty of freedom of will, or whether persistent and inveterate wickedness may be changed by the power of habit into nature, is a result which you yourself, reader, may approve of, if neither in these present worlds which are seen and temporal, nor in those which are unseen and are eternal, that portion is to differ wholly from the final unity and fitness of things. But in the meantime, both in those temporal worlds which are seen, as well as in those eternal worlds which are invisible, all those beings are arranged, according to a regular plan, in the order and degree of their merits; so that some of them in the first, others in the second, some even in the last times, after having undergone heavier and severer punishments, endured for a lengthened period, and for many ages, so to speak, improved by this stern method of training, and restored at first by the instruction of the angels, and subsequently by the powers of a higher grade, and thus advancing through each stage to a better condition, reach even to that which is invisible and eternal, having travelled through, by a kind of training, every single office of the heavenly powers. From which, I think, this will appear to follow as an inference, that every rational nature may, in passing from one order to another, go through each to all, and advance from all to each, while made the subject of various degrees of proficiency and failure according to its own actions and endeavours, put forth in the enjoyment of its power of freedom of will.