The Apology of Aristides was written in relation to the Emperor Hadrian sometime 117 and 138 (bringing it within the time frame of the Epistle of Diognetus), and not long after John’s Apocalypse. It details to the Emperor the attempts by others to find the true God, and their subsequent failures. Fore 1500 years, we had only the mention of Eusebius concerning the Apology, but it was found in the waning years of the 19th century by Armenian monks; it was then found in the Syriac version by Orthodox monks at Mt. Sinai. The Greek exists in a modified form, and cannot be trusted in the differences. Of interesting note to the discussion of the doctrinal development is from Book II. The The English translation from the Syriac reads,
The Christians, then, reckon the beginning of their religion from Jesus Christ, who is named the Son of God most High; and it is said that God came down from heaven, and from a Hebrew virgin took and clad Himself with flesh, and in a daughter of man there dwelt the Son of God. This is taught from that Gospel which a little while ago was spoken among them as being preached; wherein if ye also will read, ye will comprehend the power that is upon it. This Jesus, then, was born of the tribe of the Hebrews; and He had twelve disciples, in order that a certain dispensation of His might be fulfilled. He was pierced by the Jews; and He died and was buried; and they say that after three days He rose and ascended to heaven; and then these twelve disciples went forth into the known parts of the world, and taught concerning His greatness with all humility and sobriety; and on this account those also who to-day believe in this preaching are called Christians, who are well known. There are then four races of mankind, as I said before, Barbarians and Greeks, Jews and Christians
This statement rings true of a Modalistic viewpoint, that God robed Himself with flesh as the Son of God.