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The Israel of God was, in the First Century, made up both of the remnant of Old Covenant Israel who accepted Christ and those not of the blood line who accepted Christ. Of course, this is where Christian Zionism would disagree, and insist on another doctrine which separates believing Gentiles from believing Jews, something completely contrary to Romans 10: 12 and Galatians 3: 28.
You'll have to find a means of peace with the possible sting of the following observation...
So much for your obviously one-sided theologically biased books on the history of a thing.
Fact is that much of the tradition the Reformed Tradition is based on is the once anti-Semetic Replacement theology of many of the so called Early Church fathers.
It is theirs that had been a forced "Christian" Zionism" - as a forced replacement of God's delayed plan and purpose concerning Israel that continued with the RCC after them, and from there, with the Reformers of the Middle Ages.
A supposed "Christian" Zionism that on our shores, became a just as equally forced so called "God inspired America" as some sort of an "America as Zion" (not to be confused with the Jewish American Zionist movement).
Thus, many of of it's various laws based on the OT, and many it's places throughout the country named after; various places in the Old Testament.
And with much the same same legalistic Replacement bigotry in it's willful ignorance; a bigotry out of an ignorance of God's overall plan and purpose that continues to this very day, even in many a woefully ignorant "Dispensationalist."
I continue to find it all fascinating; but ignorantly purported America as Zion...is just that.
Jeremiah 33:23 Moreover the word of the LORD came to Jeremiah, saying, 33:24 Considerest thou not what this people have spoken, saying, The two families which the LORD hath chosen, he hath even cast them off? thus they have despised my people, that they should be no more a nation before them. 33:25 Thus saith the LORD; If my covenant be not with day and night, and if I have not appointed the ordinances of heaven and earth; 33:26 Then will I cast away the seed of Jacob, and David my servant, so that I will not take any of his seed to be rulers over the seed of Abraham, Isaac, and Jacob: for I will cause their captivity to return, and have mercy on them.