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.