Finlan devotes an entire chapter, The Sacrificial Metaphor in Roman 3:25, to a detailed analysis of a single word, hilasterion, meaning [to be] a propitiation. For Finlan, hilasterion, that also means ‘mercy seat,’ is a cultic atonement metaphor designed by Paul to be an allusion to the act of the High Priest entering the Holy of Holies on the Day of Atonement and sprinkling blood on the mercy seat. Neither Paul nor Finlan mention that it is the High Priest who is the actor in the cultic setting. Every NT writer had to deal with the question: what do we do with the High Priest and the related belief structure? We know from Philo that the ceremonial robes of the High Priest repeatedly vaunted in Hellenistic literature and interpreted in terms of cosmic symbolism endowed him with transcendent glory. The High Priest possessed by sanction of scripture the supreme power to interpret the law.[i] Furthermore, particularly Jews in the Diaspora viewed the religious duties of the High Priest in the cult as a universal saving event.[ii] Since the High Priest was viewed as “the captain of their salvation,”[iii] even a cynical Jew would want to treat the High Priest with the utmost respect. Paul treads carefully. Paul does not explicitly state that Jesus is the new High Priest.
Finlan recognizes the importance of sacrifice in understanding Paul. Finlan’s ideas need now to be supplemented by a consideration of Margaret Barker's thesis that the goat 'lyhwh' on the Day of Atonement is a substitute for the high priest (who plays the role of YHWH) in the cultic drama. It is the blood of this goat that makes the atonement (in the pre-eminent act of atonement) as a substitute for the life (i.e. Death) of the high priest/yhwh. (See e.g. M. Barker, The Revelation of Jesus Christ (Edinburgh: T. & T. Clark, 2000); The Great High Priest, The Temple Roots of Christian Liturgy (London: T. & T. Clark, 2003), chapter 3). In both books, Barker has fascinating interpretative observations on a number of late Second Temple texts to support her thesis.
For further texts relating the suffering of the high priesthood and the Day of Atonement - supportive of Barker's thesis, though not explicitly referring to atoning suffering, see C. H. T. Fletcher-Louis, "The Revelation of the Sacral Son of Man: The Genre, History of Religions Context and the Meaning of the Transfiguration," Auferstehung - Resurrection. The Fourth Durham-Tübingen-Symposium: Resurrection, Exaltation, and Transformation in Old Testament, Ancient Judaism, and Early Christianity (eds. F. Avemarie and H. Lichtenberger; WUNT 135; Tübingen: Mohr-Siebeck, 2001) 247-298 (pp. 286-88).
[i] Deut. 17:11-12; 33:10; Malachi 2:8.
[ii] Philo Spec. I.197; II 162, 165f.
[iii] Josephus, Bell. 4.318.