Three times a year, states the Testamentum Domini (1.28), the bishop is to instruct the people in the mysteries. This is to take place at Pascha, at Pentecost and at Epiphany.
The instruction concerns in particular the harrowing of hell. The only dedicated study of which I am aware is that of Jean Parisot, ”Note sur la mystagogie du “Testament du Seigneur”” Journal asiatique 9.15 (1900), 377-380, who finds some intriguing but not especially enlightening parallels.
However, this “mystagogy” is also found in the Arabic Didascalia (on which see prior posts) but most interestingly is preserved in Bohairic in the Coptic liturgy, at the consecration of the chrism. These texts are edited by O. Burmeister, “The Coptic and Arabic versions of the Mystagogia” Le Muséon 46 (1933), 203-235. What seems to me significant is the paschal context for this, as for the use in the Testamentum Domini. I am led to wonder whether this is a paschal proclamation in origin.
The “mystagogy” is, moreover, a finely-wrought bit of rhetoric:
Thus note the homoiarcton:
He is wisdom,
he is strength,
he is Lord,
he is understanding…
he is our light, salvation, saviour, protector,
helper, teacher, deliverer, rewarder,
assistance, strength, wall…
passible and impassible,
dead (yet) living,
Son of the Father,
incomprehensible and comprehensible…
Ethopoiia (as death cries out, homoiarctically by the way):
“Who is this, clothed in the humanity which was subject to me, and who has however conquered me?
Who is this who is wresting from destruction the flesh which was bound by me?
Who is this who is clothed in earth but who is yet of heaven?…”
Anyone familiar with Melito of Sardis, or indeed Polemo of Smyrna, will recognize the style.
I would hesitate to go beyond this, but am confident in claiming this as ante-Nicene, and as deriving from a paschal liturgical proclamation.