Just read a great paper on Israel and the church by Adrian Burk. He points out that while the New covenant supersedes the Mosaic covenant (making it obsolete) it fulfils the Abramic covenant.
He quotes David Bosch:
“Paul never surrenders the continuity of God’s story with Israel. The church cannot be the people of God without its linkage to Israel… The gospel means the extension of the promise beyond Israel, not the displacement of Israel by a church made up of gentiles. Paul therefore never explicitly says that the church is the “new Israel”, as becomes customary from the second century onward, for instance in the writings of Barnabus and Justin Martyr. Indeed, the church is not a new Israel, “but an enlarged Israel” and gentile Christians should never lose sight of that.” David Bosch Transforming Mission (New York: Orbis 2001) 164