In Contra Eunomium 3.9.54, Gregory of Nyssa quotes an intriguing passage by Eunomius on the topic of to tēs eusebeias mystērion (cf. 1 Tim 3:16). This passage, which follows a brief account of some of Eunomius' arguments against Basil, claims that "'the mystery of piety' is constituted neither by the solemnity of names nor by the particular character of customs and mystical symbols, but by the precision of dogmas."
In the first part of this paper, I will reconstruct, through careful analysis of Gregory's testimony and close comparison with Basil's Contra Eunomium, a plausible sketch of Eunomius' treatment of "the mystery of piety" in hisApologia Apologiae. I will also consider the possibility that Eunomius is responding not only to Basil's Contra Eunomium 2.22, which does not explicitly mention "the mystery of piety," but also to De Spiritu Sancto 27.65-68, which does.
In the second part of the paper, I will offer a detailed examination of Gregory's argument inContra Eunomium 3.9.54-64, identifying those areas in which Gregory is indebted to Basil, on the one hand, and those areas in which the younger brother innovates, on the other. I will pay special attention to how Gregory's treatment of "the mystery of piety" fits within his broader use of mystērion-language in theContra Eunomium, the frequency of which stands in marked contrast to the lack of such language in the Contra Eunomium by his brother.