The text known as the Letter to Diognetus was discovered in 1436 by a Catholic priest, Thomas d'Arezzo, in a fish market in Constantinople. The existence of the unique manuscript, the absence of reference to the author, and the lack of contemporary or later patristic references to the text led many researchers to consider it a forgery, while others argued that it was a text written for impressing purposes.
In the introduction of the letter, the author poses three questions about which Diognetus wants to be better informed:
◆What is the identity of the God of Christians?
◆What is the origin of this excessive love they show towards their neighbor? and
◆Why did their faith appear so late in the world?
In answering these questions, the author will criticize both idolatry and the erroneous views of the Jews regarding the worship of God. He will then refer to the way of life of Christians who, although they live on earth like everyone else, are already citizens of Heaven as they are members of the Church. In the following chapters, he will present the Christian teaching about God, while simultaneously criticizing the views of various philosophers. As for the question of the delayed presence of Christian faith in the world, the author will say that God's redemptive plan through His Son was realized when man realized that he could not be saved on his own.