Athanasius, the "Father of Orthodoxy" (The Athanasian Creed) says that what futurists are waiting for has ALREADY OCCURRED... "The earth IS ALREADY 'filled with the knowledge of the Lord' in fulfillment of Isaiah 11:9 and Habakkuk 2:14; and DEATH IS ALREADY DESTROYED among believers in FULFILLMENT of First Corinthians 15:55" ~ Athanasius, Festal Letter (4th century AD)Documentation
The quote above (as found on a hyper-preterist Facebook page) cites "Athanasius, Festal Letter (4th century AD)." The first problem with this reference is that there are multiple festal letters from Athanasius. The second problem is I could not locate any corroboration that the documentation to a Festal Letter is accurate.
After searching around a bit, I would posit the quote in this form is from the hyper-preterist book, House Divided Bridging the Gap in Reformed Eschatology A Preterist Response to When Shall These Things Be? It occurs in the exact form in Chapter Two: If Preterism is True by David A. Green. The contents of this chapter can be found here, posted in this discussion thread by (who appears to be) the author. Mr Green states,
Despite futurist errors regarding various and major prophecy-texts, the church has been, in a very real sense, teaching preterism for nearly two thousand years now. We can find examples of preterism throughout the church fathers...The quote is not from a Festal Letter, since Mr. Green goes on to present a section specific to the Festal Letters. In fact, the quote isn't an Athanasius quote at all, but is rather a summary of statement Mr. Green put together from On the Incarnation and the Festal Letters as to what he think Athanasius believed. In other words, each statement represents a quote from Athanasius. Scrolling through the quotes used by Green, these were the references he gives:
The Father of Orthodoxy himself, Athanasius (AD 293-373), is a remarkable example of this same phenomenon. We can see from the following excerpts from his On the Incarnation and his Festal Letters, that although Athanasius believed in a yet-future Second Coming and in a Resurrection of the Flesh, he also believed the following: The earth is already filled with the knowledge of the Lord (the gospel) in fulfillment of Isaiah 11:9 and Habakkuk 2:14; and Death is already destroyed among believers in fulfillment of 1 Corinthians 15:55 (O death, where is your sting? O grave, where is your victory?).
"The earth is already filled with the knowledge of the Lord" is from On the Incarnation, 16:3; 40,6-7; 45, 5-6; 48,4; 50,1; 55,3
"Death is destroyed" is from On the Incarnation, 9,4; 27.1, 3-4; 29.5; 31,3; Festal Letter IV,3; VI,9; VI,10
It would certainly be time-consuming to go through each quote cited by Mr. Green. Some of the citations say nothing more than Christ conquered death by his resurrection. Others say nothing more than the Messiah has come and the Jews are wrong to look for a future Messiah: the prophecies as to his coming have been fulfilled. One quote says nothing more than the knowledge of God pervades all of creation.