It's mercy from the very beginning!

Paul’s construal of the calling of the patriarchs (9:6–13) suggests a subtle difference: mercy goes all the way down to the origin and the root, as the very source of Israel’s history. In this sense, mercy is for Paul not just restorative, but creative: it brings into being what was otherwise impossible, creating not just “reconciliation” but “life from the dead” (11:15). As in LAB [Pseudo-Philo], God’s mercy is incongruous with the worth of its recipients; Romans 9–11 suggests that this is so not only because it has to be (in the face of universal disobedience) but because it was ever so even in the formation of Israel, and will remain so in the salvation of both Gentile and Jew.—J. M. G. Barclay, Paul and the Gift, 327