Outside of the initial, flustered incomprehension upon considering the concept of predestination for the first time, the most common knee-jerk objection to Calvinism among mainstream Evangelicalism has got to be over "replacement theology." The impression out there among the percentage who know of Calvinism's existence seems to be that all Calvinists think that Israel has been utterly cut off and consigned to the outer darkness. Given that a healthy percentage of Protestants ingest Dispensational presupps (along with cookies and juice) from their earliest days in Sunday School, this is quite a deterrent to accepting the truth of Reformed belief.
Reformed Christians actually maintain a balanced view between the bifurcation of Dispensationalism amd the excision of Replacement theology. Richard Pratt, of RTS, has put together a great piece entitled To The Jew First: A Reformed Perspective that's a great clarifier. A good supplement would be Fred Klett's Not Replacement... Expansion! Both of these come from Monergism.com's site. If you've never checked out monergism, take a peek. It's huge. Beyond huge. In the words of the dad in "So I Married an Ax-Murderer" -- It's a virtual planetoid! It's got its own weather-systems!
Here are Calvin's thoughts on the subject (Israel, not Mike Myers films):
"I extend the word Israel to all the people of God, according to this meaning, -When the Gentiles shall come in, the Jews also shall return from their defection to the obedience of faith; and thus shall be completed the salvation of the whole Israel of God, which must be gathered from both; and yet in such a way that the Jews shall obtain the first place, being as it were the first born in God's family."
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For anyone interested in keeping up with events in the church around the world, check out Brigada's mission mobilization newbriefs. Caleb Project and Brigada were both big influences on the Duchess and I as we considered overseas ministry.