Israel of God refers to Jewish people who received Christ as their Savior and consequently belong to the church. It does not refer to the entire church.
When that idea comes about, this view then in effect says that the church constitutes the true and only Israel today and that, hereafter, Christians become “spiritual Israel” or “spiritual” Jews, and all New Testament promises concerning Israel will be fulfilled in the church and do not apply to ethnic Jewish people or the literal nation of Israel.