Matthew and the parting of the ways

Anders Runesson's essay, "From Where? To What? Common Judaism, Pharisees, and the Changing Socioreligious Location of the Matthean Community" (Common Judaism: Explorations in Second-Temple Judaism, edited by Wayne O. McCready and Adele Reinhartz [Minneapolis: Fortress Press, 2008], 97–113), is as awkward as its title. I think I'm sympathetic to his overall thesis, but it isn't easy to tell.

But his final paragraph uses a familiar phrase in a peculiar way:

In conclusion, the Gospel of Matthew provides us with early evidence of an inner-Jewish parting of the ways, very different in character from the process that much later would lead to the establishment of "Christianity" as a religion independent of "Judaism." Indeed, the use of the Gospel of Matthew by non-Jewish Christ-believers as a resource in that later process of identity formation is a fascinating and hermeneutically complex problem that deserves further study. (113)

My question: How helpful is it to refer to "an inner-Jewish parting of the ways"? The point is clear enough: the Matthean community (if we can still speak of a "Matthean community") split from a[nother] Jewish group rather than from Judaism itself. But the metaphor parting of the ways has been used historically to refer to the differentiation and dis-identification of Jewish ways of being from their Christian counterparts, and vice versa. If Matthew presents evidence of and for continued Jewish identities for those who found their traditions in its telling of Jesus' story, shouldn't we jettison parting of the ways language tout court?

Justin and the rhetoric of movement

Once again I'm well outside my area of expertise; I would value any comment from those of you with knowledge of (i) Justin Martyr, (ii) second-century Judaism and Christianity, or (iii) the so-called "parting of the ways."

I'm reading Jan-Eric Steppa's essay, "The Reception of Messianism and the Worship of Christ in the Post-Apostolic Church" (The Messiah in Early Judaism and Christianity [ed. M Zetterholm; Minneapolis: Fortress Press, 2007], 79–116). In his discussion of "Justin Martyr's Messiah" (85–89) Steppa suggests that the early church (or at least Justin) conceived of God's favor as moving from Judaism to Christianity.

For Justin, the failure of the Jews to comprehend the numerous scriptural evidences for the messiahship of Jesus completely disqualified them from possession of the Scriptures. Justin expresses here an uncompromising view of the transference of God's favor from the Jews to the Christians. From the moment of the Jews' rejection of Christ as the Messiah, Christians have become the rightful descendants of Judah, Jacob, Isaac, and Abraham, and thus the true spiritual Israel. (88; my emphasis)

I can't help but perceive some disjunction between the first sentence and the second, italicized sentence. Without any extensive knowledge of Justin, I'm wondering if Justin's rhetoric assumes a movement of the Jews from inside God's favor—descendants of the Patriarchs, possessors of the holy scriptures, etc.—to outside God's favor on account of their rejection of Jesus as Israel's messiah. As such (and in agreement with that first sentence), the Jews have forsaken their birthright, including (but not limited to) their right to the scriptures.

But does this necessarily equate a movement of God's favor from Israel to the church? Or does Justin conceive of the church as a static entity upon which God's favor rests (perhaps that entity to which the label Israel applies), into which those gentiles who accept the gospel and out of which those Jews who reject the gospel are transferred? In other words, is the church/Israel in Justin's universe less the heir of the scriptures and other symbols of God's favor and more their original possessors? And are the Jews less those whom God's favor has abandoned and more those who have abandoned God's favor (/messiah)?

My instinct is that, if the answers to these questions are "Yes," then these are distinctions that matter. Again, if this is a helpful way to think about Justin, then we need to be more precise about what/who moves, from/to where, and what the consequences of that movement might be.