Is the dichotomy between Jewish and Christian a valid one in this context? Paul’s argument in Romans and Galatians would appear to be that the calling of and promise to Abraham persists regardless of whether it takes a distinctively Jewish form or not.

The answer to this, I think, depends on what one means. Obviously, a person who is a Jew but does not accept Jesus as the Messiah might see himself in continuity with Abraham, but someone else could say he isn’t actually in continuity with the “true” Abrahamic narrative in a way that might classify him as “emergent theologian.”

I speak of “Jew” and “Christian” (and “Muslim” for that matter) as a way of pointing to the ambiguity of “people of God.” Many would claim to be people of God that would not recognize Jesus as Lord; while their perspective may inform emergent theology, I am not sure they would identify themselves as emergent theologians.

Finally, I found the phrasing “the calling of Abraham to be blessed and be a blessing to the nations of the world” to place the onus of blessing less on God than, say, “the promise to bless Abraham and, through him, to bless the nations of the world.” I could see how your syntax could be interpreted to mean that God’s purpose in calling Abraham was to bring blessing to Abraham and the world, but that interpretation was not the most obvious one to me.