Rufino de Aquilea
Origen's "On the First Principles" was the first ever systematic exposition of Christian theology. He composed it as a young man between 220 and 230 while he was still living in Alexandria. Fragments from Books 3.1 and 4.1–3 of Origen's Greek original are preserved in Origen's "Philokalia". A few smaller quotations of the original Greek are preserved in Justinian's "Letter to Mennas". The vast majority of the text has only survived in a heavily abridged Latin translation produced by Tyrannius Rufinus in 397. "On the First Principles" begins with an essay explaining the nature of theology. Book One describes the heavenly world and includes descriptions of the oneness of God, the relationship between the three persons of the Trinity, the nature of the divine spirit, reason, and angels. Book Two describes the world of man, including the incarnation of the Logos, the soul, free will, and eschatology. Book Three deals with cosmology, sin, and redemption. Book Four deals with teleology and the interpretation of the scriptures.